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United States Patent
4893335
Fuller , ; et al.
January 9, 1990
Title
Remote access telephone control system
Abstract
A telephone control system connects to the telephone line from a telephone exchange. The control system includes a detector for detecting signals on the line, a signal generator for producing and applying control signals to the telephone line, memory for storing electronic signals and a central processor for monitoring signals on the line as detected by the detector, accessing the memory to produce and apply control signals to the signal generator. The control system is programmable to provide a variety of controllable functions to a remote user including activation of the conferencing/transferring function provided by the telephone exchange to allow a user to sequentially complete successive phone calls through the control system without the user hanging-up, or to redirect calls to pre-programmed, remotely controllable numbers. In addition, the control system is capable of receiving, storing and redirecting messages to pagers.
Inventors:
Fuller; Robert M.
(Redmond,
WA
)
, Epler; Frederick A.
(Issaquah,
WA
)
, Manowski; Maxwell E.
(Enumclaw,
WA
)
Assignee:
Fuller Research and Development Company
(Bellevue,
WA
)
Appl. No.:
841931
Filed:
March 20, 1986
Current U.S. Class:
379/200
379/207.06
379/207.07
379/211.02
379/212.01
379/355.03
379/88.15
379/88.21
379/911
379/914
379/199
Field of Search:
179/2A,2AM,5R,5P,5.5,6.02,18BC,18BD,18BE,37,84C,9B,9D,99A,18BF 379/40,51,57,69,95,102,105,107,142,157,158,159,167,188,199,200,202,204,205,210
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DE
Other References
Kopec et al., "Electronic Business Telephone", GTE Electric Journal, Mar. 1980, pp. 34-40. .
Popular Science, Jun. 1981, p. 1 Advertisement: "Zap your Mom", by JS & A Products, Northbrook, Il..~
Primary Examiner:
George; Keith E.
Attorney, Agent or Firm:
Hamley; James P.
Parent Case Text
This is a continuation-in-part of now abandoned U.S. application Ser. No. 650,821, filed Sept. 14, 1984, entitled "TELEPHONE CONTROL SYSTEM", invented by the same inventors and assigned to the same assignee as herein .
Claims
We claim:
1. A telephone control system connected between a telephone line and a local telephone station, said system comprising:
a decoder for determining numbers being dialed by said local station and outputting information signals corresponding thereto;
a dialer selectively placing on said telephone line dialing signals corresponding to digit identifying signals;
processor means receiving the information signals from said decoder, said processor means examining information signals corresponding to numbers being dialed, determining if said information signals have a predetermined value, recording the information signals for numbers being dialed at least up until the time that said processor means determines if a call over said telephone line is being attempted and, in response to said processor means determining that a call over said telephone line is being attempted and within a period thereafter that is independent of the rate of subsequently dialing digits, outputting to said dialer digit identifying signals corresponding to the information signals recorded by said processor means at least up until the time that said processor means has determined that a call over said telephone line is being attempted thereby placing dialing signals corresponding to said information signals on said telephone line; and
a switch actuatable to a first position in which said telephone station is connected to said telephone line, said switch being actuated by said processor means to said first position responsive to said processor means determining that a call over said telephone line is being attempted and after said processor means has outputted to said dialer the digit identifying signals corresponding to all information signals recorded in said processor means prior thereto, whereby after said switch has been activated to said first position, said dialing signals are thereafter placed on said telephone line in real time as they are generated by said local telephone station.
2. The telephone control system of claim 1, further including a memory recording a plurality of said information signals corresponding to respective telephone numbers, said memory selectively outputting said identifying signals to said processor means.
3. The telephone control system of claim 1 wherein said processor means includes memory means for recording a number previously dialed by the local station and timing means for periodically causing said processor means to output to said dialer digit identifying signals corresponding to the number recorded in said memory means.
4. The telephone control system of claim 3 further including means for recognizing that the telephone station corresponding to said digit identifying signals has gone off hook and, in response thereto, for preventing dialing signals from being thereafter generated on said telephone trunk line by said dialer until the telephone station corresponding to said digit identifying signals has gone on hook.
5. The telephone control system of claim 1 further including memory dial means, comprising:
storage means for recording the digits of a plurality of telephone numbers and at least one dial mode identifier code interspersed among the digits of at least some of said telephone numbers for identifying a dual-tone multifrequency dialing mode or a dial-pulse dialing mode;
selector means for selecting a telephone number corresponding to a digit dialed by said local telephone station; and
means for applying to said dialer digit identifying signals corresponding to the digits of the selected telephone number and dial codes interspersed among the digits of the selected telephone number, said dialer being responsive to said dial codes to place on said telephone line dual-tone multifrequency tones corresponding to said digit identifying signals subsequent to dual-tone multifrequency dial mode identifier codes being applied to said dialer and to place dial pulses corresponding to said digit identifying signals subsequent to dial pulse dial mode identifier codes being applied to said dialer whereby telephone numbers recorded in said storage means may be dialed in any combination of dial pulses and dual-tone multifrequency tones.
6. The telephone control system of claim 1 further including memory dial means, comprising:
storage means for recording the digits of a plurality of telephone numbers and at least one dial pause identifier code interspersed among the digits of at least some of said telephone numbers;
selector means for selecting a telephone number corresponding to a digit dialed by said local telephone station;
a supervisory signal detector for detecting a predetermined supervisory signal on said telephone line and outputting a supervisory signal detection indication in response thereto;
means for applying to said dialer digit identifying signals corresponding to the digits of the selected telephone number and pause identifier codes interspersed among the digits of the selected telephone number, said dialer applying to said telephone line dialing signals corresponding to the digits of the selected telephone number until a pause identifer code is received, said dialer applying to said telephone line dialing signals corresponding to the digits of the selected telephone number upon receipt of a supervisory signal detection indication from such supervisory signal detector.
7. A telephone control system connected between a telephone line and a local telephone station, said station comprising: switch means actuated by an off-hook signal for decreasing the impedance between terminals of said control system that are connected to said telephone line:
processor means for momentarily terminating said off-hook signal while a first telephone station is connected to said local telephone station to generate a first hook-flash signal, then allowing a telephone number for a second telephone station to be dialed on said telephone line and then once again momentarily terminating said off-hook signal to generate a second hook-flash signal suitable for causing said first telephone station to be connected to said second telephone station;
storage means for recording the telephone number for said second telephone station;
a dialer receiving an output from said storage means, said dialer being responsive to an initiate signal for applying dialing signals to said telephone line that correspond to the telephone number for said second telephone station;
a ring detector for detecting a ring signal on said telephone line and for generating a ring detect signal in response thereto, wherein said processor means receives an output from said ring detector and generates said off-hook signal in response to said ring detect signal thereby taking said local telephone station off-hook, said processor means further generating in sequence said first hook-flash signal, said initiate signal and said second hook-flash signal thereby forwarding the call placed by said first telephone station to said second telephone station;
and wherein said storage means records a plurality of telephone numbers associated with respective second telephone stations, said system further including a decoder for decoding dialing signals on said line to determine a number being dialed by said first telephone station, wherein said processor means receives an output from said decoder and causes said dialer to apply dialing signals to said line corresponding to a telephone number recorded in said storage means, said telephone number being designated by a respective number being decoded by said decoder thereby forwarding the telephone call placed by said first telephone station to one of several second telephone stations depending upon the number being dialed by said first telephone station.
8. The telephone control system of claim 7 further including said decoder determines numbers being dialed by said local telephone station, and wherein said processor means receives an output from said decoder and generates said first hook-flash signal responsive to said local station dialing a predetermined number and then outputs a dial tone to said local telephone station, said telephone number for said second telephone station being dialed by said local telephone station thereby initiating a conference telephone call between said local, first and second telephone stations.
9. The telephone control system of claim 7 wherein said decoder further comprises means for decoding a telephone number dialed by said first telephone station and wherein said processor means receives an output from said decoder and replaces a predetermined telephone number recorded in said storage means with a telephone number dialed by said first telephone station in the event that said telephone number includes a predetermined access code thereby remotely modifying the telephone station to which calls subsequently placed to said local station are forwarded.
10. The telephone control system of claim 7 wherein said decoder further comprises means for decoding a telephone number dialed by said first telephone station and wherein said processor means receives an output from said decoder and, in the event that said telephone number includes a predetermined access code, causes said storage means to record the telephone number dialed by said first telephone station, generates said first hook-flash signal, generates said initiate signal to cause said dialer to apply dialing signals to said telephone line that correspond to the telephone number dialed by said first telephone station and recorded in said storage means and then generates said second hook-flash signal to connect said first telephone station to the station dialed by said first station thereby allowing said first station to dial telephone stations through said local telephone station.
11. The telephone control system of claim 7 further including an answering machine connected to the local station telephone line and wherein said processor means delays generating said initiate signal until after said answering machine has recorded a message from said first telephone station and broadcast a message to said first telephone station.
12. The telephone control system of claim 7 wherein said storage means further records the telephone number of a telephone paging station, wherein said dialer applies dialing signals to said telephone trunk line that correspond to the telephone number for said paging station in response to a page alert signal and wherein said processing means generates said page alert signal prior to generating said initiate signal.
13. The telephone control system of claim 12 further including an answering machine connected to the local station telephone lines and wherein said processor means delays generating said page alert signal and said initiate signal until after said answering machine has recorded a message from said first telephone station and/or broadcast a message to said first telephone station.
14. The telephone control system of claim 7 wherein the decoder further comprises means for decoding dialing signals on said line to determine a number being dialed by said first telephone station, and wherein said processor means generates said initiate signal only if a predetermined number is decoded by said decoder thereby forwarding the telephone call placed by said first telephone station to said second telephone station only in response to a predetermined number being dialed by said first telephone station.
15. The telephone control system of claim 7 further including an answering machine connected to the local station telephone line and wherein said processor means delays generating said initiate signal until after said answering machine has broadcast a list of call forwarding destinations and corresponding call forwarding codes that may be dialed by said first station.
16. A system for reporting to a central telephone station the telephone number associated with a telephone unit having an identifying number and being connected to a telephone line, comprising:
inhibit means for rendering said telephone unit inoperable until the telephone number associated with said telephone unit has been entered into said telephone unit;
storage means for storing the telephone number associated with said telephone unit; and
dialing means for automatically causing said telephone unit to dial the telephone number of said central telephone station and, after said central telephone station has gone off-hook, dialing the telephone number associated with said telephone unit and a number corresponding to said identifying number thereby informing said central telephone station the telephone number to which said telephone unit is connected.
17. The telephone control system of claim 1 further including a supervisory signal detector for detecting a predetermined supervisory signal on said line and outputting a supervisory signal detection indication to said processor means responsive thereto and wherein said processor means initiates recording the digits being dialed by said local station and actuates said switch from said first position after a predetermined number of digits have been dialed by said local station and at least up until said supervisory signal detector outputs said supervisory signal detection indication and, in response to said supervisory signal detection indication, outputting to said dialer digit identifying signals corresponding to the digits recorded by said processor means after said predetermined number of digits have been dialed by said local station and at least until the time that said processor means receives said supervisory signal detection indication, said processor means then actuating said switch to said first position so that said dialing signals are thereafter placed on said telephone line as they are generated by said local telephone station.
18. A remotely accessible telephone control system for connection to a telephone line from a telephone exchange, the telephone exchange providing a user controlled call conferencing function, the system comprising:
detector means for detecting signals on said telephone line;
signal generating means responsive to control signals to produce predetermined signals and apply said signals to said telephone line;
memory means for controllably storing electronic signals; and
central processing means for monitoring signals on said telephone line as detected by said detector means, accessing said memory means and producing and applying predetermined control signals to said signal generating means, said central processing means including means for:
(a) identifying a call to said system from a remote user,
(b) identifying a control signal from said remote user indicating a desired call transfer to a predetermined number,
(c) receiving and storing said predetermined transfer number from said remote user,
(d) activating the call conferencing function of the telephone exchange to place the remote user on hold,
(e) producing control signals to cause the signal generating means to apply appropriate signals to said telephone line to complete a call to said predetermined transfer number,
(f) further activating said telephone exchange to connect said remote user to said predetermined transfer number,
(g) detecting the completion of the call between said remote user and said transfer number and, in response thereto,
(h) repeating items (b) through (f) to allow said remote user to call a further transfer number.
19. The system of claim 18 wherein item (g) further comprises means for detecting the absence of an audio signal on the connection between said remote user and the transfer number for a predetermined time period.
20. The system of claim 18 wherein item (g) further comprises means for ignoring a momentary disconnection on the line between said remote user and said transfer number caused by a transient event.
21. The system of claim 19 wherein item (g) further comprises means for ignoring a momentary disconnection on the line between said remote user and said transfer number caused by a transient event.
22. The system of claim 18 wherein item (g) further comprises means for detecting a disconnection on the line between said remote user and said transfer number and then maintaining a connection to said remote user for a predetermined time period, thereby allowing the remote user time to initiate a further transfer call per item (h).
23. The system of claim 21 wherein item (g) further comprises means for detecting a disconnection on the line between said remote user and said transfer number and then maintaining a connection to said remote user for a predetermined time period, thereby allowing the remote user time to initiate a further transfer call per item (h).
24. The system of claim 18 wherein said telephone exchange further provides a "call waiting" function, the central processing means further comprising means for detecting an incoming call while a remote user-to-transfer call is in operation and causing said signal generating means to return a busy signal to said incoming caller.
25. A remotely accessible telephone control system for connecting to a telephone line from a telephone exchange, the telephone exchange providing a user controlled call conferencing function, the system comprising:
detector means for detecting signals on said telephone line;
signal generating means responsive to control signals to produce predetermined signals and apply said signals to said telephone line;
memory means for controllably storing electronic signals; and
central processing means for monitoring signals on said telephone line as detected by said detector means, accessing said memory means and producing and applying predetermined control signals to said signal generating means, said central processing means including means for:
(a) identifying a call to said system from a remote user,
(b) activating the call conferencing function of the telephone exchange to place the remote user on hold,
(c) recalling from said memory means a predetermined transfer number,
(d) producing control signals to cause the signal generating means to apply appropriate signals to said telephone line to complete a call to said predetermined transfer number,
(e) further activating said telephone exchange to connect said remote user to said predetermined transfer number,
(f) identifying a call from a remote user indicating a desired change in said predetermined transfer number,
(g) receiving from said remote user the new transfer number, and
(h) loading into said memory said new predetermined number.
26. The system of claim 25 wherein the central processing means further includes means for:
(i) disconnecting said system from said remote user-to-transfer number connection while maintaining said remote user to transfer number connection such that said system is free to process other incoming calls.
27. The system of claim 25 wherein the central processing means further includes means for (i) detecting the completion of the call between said remote user and said transfer number.
28. The system of claim 27 wherein item (i) further comprises means for detecting the absence of an audio signal on the connection between said remote user and the transfer number for a predetermined time period.
29. The system of claim 27 wherein item (i) further comprises means for ignoring a momentary disconnection on the line between said remote user and said transfer number caused by a transient event.
30. The system of claim 28 wherein item (i) further comprises means for ignoring a momentary disconnection on the line between said remote user and said transfer number caused by a transient event.
31. The system of claim 25 wherein said telephone exchange further provides a "call waiting" function, the central processing means further comprising means for detecting an incoming call while a remote user-to-transfer call is in operation and causing said signal generating means to return a busy signal to said incoming caller.
32. The system of claim 25 wherein said central processing means further includes means for causing said signal generating means to apply an artificial ring-back signal on the line to said remote user prior to item (b) such that the remote user has reduced awareness of the transfer operation.
33. The system of claim 32 wherein said central processing means causes said artificial ring signal to be produced with similar cadence as an actual ring signal.
34. A remotely accessible telephone control system for connection to at least one telephone line from a telephone exchange, the telephone exchange providing a user controlled call function including call conferencing, the system comprising:
detector means for detecting signals on a telephone line;
signal generating means responsive to control signals to produce predetermined signals and apply such signals to said telephone line;
memory means for controllably storing electronic signals; and
central processing means for monitoring signals on said telephone line as detected by said detector means, accessing said memory means and producing and applying predetermined control signals to said signal generating means, said central processing means including means for:
(a) identifying a call to said system from a remote user via said telephone exchange;
(b) identifying a desired call control function;
(c) producing control signals to cause the signal generating means to apply all appropriate signals to said telephone line to accomplish said desired call control function while maintaining said remote user call to said telephone exchange;
(d) activating the call conferencing function of the telephone exchange to place the remote user on hold;
(e) recalling from said memory means a predetermined transfer number;
(f) producing control signals to cause the signal generating means to apply appropriate signals to said telephone line to complete a call to said predetermined transfer number;
(g) further activating said telephone exchange to connect said remote user to said predetermined transfer number;
(h) identifying a call from a remote user indicating a desired change in said predetermined transfer number;
(i) receiving from said remote user the new transfer number; and
(j) loading into said memory means said predetermined transfer number.
35. The remotely accessible telephone control system of claim 34 wherein the central processing means further comprises means for:
(k) identifying a control signal from said remote user indicating the desired call transfer to a predetermined number;
(l) receiving and storing said predetermined transfer number from said remote user;
(m) activating the call conferencing function of the telephone exchange to place the remote user on hold;
(n) producing control signals to cause the signal generating means to apply appropriate signals to said telephone line to complete a call to said predetermined transfer number; and
(o) further activating said telephone exchange to connect said remote user to said predetermined transfer number.
36. The remotely accessible telephone control system of claim 35 wherein the central processing means further includes means for;
(p) disconnecting said system from said remote user-to-transfer number connection such that said system is free to process other incoming calls.
37. The remotely accessible telephone control system of claim 35 wherein the central processing means further includes means for:
(p) detecting the completion of the call between said remote user and said transfer number and, in response thereto;
(q) repeating items (k) through (o) above to allow said remote user to call a further transfer number.
38. The remotely accessible telephone control system of claim 37 wherein item (i) further comprises means for detecting the absence of an audio signal on the connection between said remote user and the transfer number for a predetermined time period.
39. The remotely accessible telephone control system of claim 35 wherein said telephone exchange further provides a "call waiting" function, the central processing means further comprising means for detecting an incoming call while a remote user-to-transfer call is in operation and causing said signal generating means to return a busy signal to said incoming caller.
40. The remotely accessible telephone control system of claim 34 wherein the central processing means further includes means for:
(k) disconnecting said system from said remote user-to-transfer number connection such that said system is free to process other incoming calls.
41. The remotely accessible telephone control system of claim 34 wherein said central processing means further includes means for causing said signal generating means to apply an artificial ring-back signal on the line to said remote user prior to item (c) such that the remote user has reduced awareness of the transfer operation.
42. The remotely accessible telephone control system of claim 41 wherein said central processing means causes said artificial ring signal to be produced with similar cadence as an actual ring signal.
43. The remotely accessible telephone control system of claim 34 wherein said control processing means further comprises means for:
(k) activating said signal generating means to transmit a message to a remote user allowing said user to transmit a message on the line;
(l) storing a remote user transmitted message in said memory means;
(m) terminating the connection to said remote user;
(n) recalling from said memory means a predetermined pager access service number;
(o) causing said signal generating means to complete a call to said predetermined pager access service number;
(p) recalling said remote user transmitted message from memory; and
(q) causing said signal generating means to transmit said remote user transmitted message to said pager access service number, whereby said pager access service is activated to transmit said remote user transmitted message to a predetermined pager.
44. The remotely accessible telephone control system of claim 43 wherein said central processing means further includes means for:
(r) recalling from said memory means a predetermined terminating control signal; and
(s) causing said signal generating means to transmit said predetermined terminating control signal to said pager access service following transmission of said remote user transmitted number.
45. A remotely accessible telephone control system for connection to at least one telephone line from a telephone exchange, the telephone exchange providing a user controlled call function including call conferencing, the system comprising:
detector means for detecting signals on a telephone line;
signal generating means responsive to control signals to produce predetermined signals and apply such signals to said telephone line;
memory means for controllably storing electronic signals; and
central processing means for monitoring signals on said telephone line as detected by said detector means, accessing said memory means and producing and applying predetermined control signals to said signal generating means, said central processing means including means for:
(a) identifying a cell to said system from a remote user via said telephone exchange;
(b) identifying a remote user desired call control function;
(c) producing control signals to cause the signal generating means to apply all appropriate signals to said telephone line to accomplish said desired call control function while maintaining said remote user call to said telephone exchange;
(d) activating the call conferencing function of the telephone exchange to place the remote user on hold;
(e) recalling from said memory means a predetermined transfer number;
(f) producing control signals to cause the signal generating means to apply appropriate signals to said telephone line to complete a call to said predetermined transfer number;
(g) further activating said telephone exchange to connect said remote user to said predetermined transfer number;
(h) identifying a call from a remote user indicating a desired change in said predetermined transfer number;
(i) receiving from said remote user the new transfer number; and
(j) loading into said memory means said predetermined transfer number.
46. The remotely accessible telephone control system of claim 45 wherein the central processing means further comprises means for:
(k) identifying a control signal from said remote user indicating a desired call transfer to a predetermined number;
(l) receiving and storing said predetermined transfer number from said remote user;
(m) activating the call conferencing function of the telephone exchange to place the remote user on hold;
(n) producing control signals to cause the signal generating means to apply appropriate signals to said telephone line to complete a call to said predetermined transfer number; and
(o) further activating said telephone exchange to connect said remote user to said predetermined transfer number.
47. The remotely accessible telephone control system of claim 46 wherein the central processing means further includes means for:
(p) disconnecting said system from said remote user-to-transfer number connection such that said system is free to process other incoming calls.
48. The remotely accessible telephone control system of claim 46 wherein the central processing means further includes means for:
(p) detecting the completion of the call between said remote user and said transfer number and, in response thereto;
(g) repeating items (k) through (o) above to allow said remote user to call a further transfer number.
49. The remotely accessible telephone control system of claim 48 wherein item (p) further comprises means for detecting the absence of an audio signal on the connection between said remote user and the transfer number for a predetermined time period.
50. The remotely accessible telephone control system of claim 46 wherein the telephone exchange further provides a "call waiting" function, the central processing means further comprising means for detecting an incoming call while a remote user-to-transfer call is in operation and causing said signal generating means to return a busy signal to said incoming caller.
51. The remotely accessible telephone control system of claim 45 wherein the central processing means further includes means for:
(k) disconnecting said system from said remote user-to-transfer number connection such that said system is free to process other incoming calls.
52. The remotely accessible telephone control system of claim 45 wherein the telephone exchange further provides a "call waiting" function, the central processing means further comprising means for detecting an incoming call from an incoming caller while a remote user-to-transfer call is in operation and causing said signal generating means to return a busy signal to said incoming caller.
53. The remotely accessible telephone control system of claim 45 wherein said central processing means further includes means for causing said signal generating means to apply an artificial ring-back signal on the line to said remote user prior to item (c) such that the remote user has reduced awareness of the transfer operation.
54. The remotely accessible telephone control system of claim 53 wherein said central processing means causes said artificial ring signal to be produced with similar cadence as an actual ring signal.
55. The remotely accessible telephone control system of claim 45 wherein said control processing means further comprises means of:
(k) activating said signal generating means to transmit a message to a remote user allowing said user to transmit a message on the line;
(l) storing a remote user transmitted message in said memory means;
(m) terminating the connection to said remote user;
(n) recalling from said memory means a predetermined pager access service number;
(o) causing said signal generating means to complete a call to said predetermined paper access service number;
(p) recalling said remote user transmitted message from memory; and
(q) causing said signal generating means to transmit said remote user transmitted message to said pager access service number, whereby said pager access service is activated to transmit said remote user transmitted message to a predetermined pager.
56. The remotely accessible telephone control system of claim 55 wherein said central processing means further includes means for:
(r) recalling from said memory means a predetermined terminating control signal; and
(s) causing said signal generating means to transmit said predetermined terminating control signal to said pager access service following transmission of said remote user transmitted number.
Description
TECHNICAL FIELD
This invention relates to telephone equipment and, more particularly, to a control system for a telephone line that performs switching and supervisory functions to enhance the functions of telephone stations connected to the telephone line.
DESCRIPTION OF THE PRIOR ART
Single line telephone equipment commonly used in residences and small businesses is capable of providing relatively few functions. Such systems can universally place and receive telephone calls, and a few additional features have recently become available. One of these features is "three-way calling" in which a party can initiate a call with two other parties Three-way calling is initiated by placing one of the parties on temporary hold by flashing the hookswitch. Flashing the hookswitch also obtains a dial tone. The telephone number of the second party is then dialed and the hook switch is once again flashed to retrieve the first party.
Another feature that has recently become available to single line telephone subscribers is "call waiting" in which a party is advised by an audible signal on the line that a third party is attempting to place a call to the party. The original party can then be placed on hold while the call from the third party is answered. Finally, a "speed dialing" feature has recently become available by which a party can record in the telephone central office frequently called numbers and then automatically dial those numbers by pressing two keys on the telephone set.
At the present time, the above described features are the only features that are generally available to single line telephone parties. A large number of other features are generally available to users of multi-line PBX and key telephone systems. These users are generally medium to large businesses. In addition to the features described above as being available to single line telephone parties, PBX and key telephone systems generally provide a "redial" feature in which the previously dialed number can be automatically redialed by pressing a single button, "automatic callback" in which internal lines in a PBX installation that are busy when an internal call is placed are automatically redialed when the called station is no longer busy, "toll call restriction" in which all or some of the stations in a system are prevented from dialing long distance calls having numbers beginning with "1" or "0", "intercom" in which stations in an installation can talk to each other and "call forwarding" in which a call directed to one station in the system is automatically rerouted to another station in the system or to an external telephone number.
While the above described features available for PBX and key telephone systems are not generally available to s ingle line telephone subscribers, unit are commercially available that can provide speed dialing and automatic call back features for single line telephone subscribers. However, these add-on units do not provide the other functions available in PBX and key telephone systems. Furthermore, there are a large number of useful features that are not even available in existing PBX and key telephone systems.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a single line telephone subscriber with all of the features available in the PBX and key telephone systems.
It is another object of the invention to provide a telephone control system that is capable of performing useful functions that are not presently available in any telephone system.
It is another object of the invention to provide a telephone switching system that utilizes features available with existing single line telephone line service to perform functions normally requiring multiple lines.
It is a further object of the invention to provide a telephone control system that enhances the usefulness of such telephone accessories as conventional pagers and answering machines.
It is still another object of the invention to provide a telephone control system of the character described that can be easily and quickly installed in virtually any single line, telephone system.
These and other objects of the invention are provided by a telephone control system housed in a thin rectangular box on which telephone set may be placed. The control system includes a central processing unit that interfaces with the other components of the system. These other components include a line current detector detecting line current in the telephone line, a ring detector detecting a ring on the telephone line, a dial pulse generator selectively varying the telephone line impedance in a pulsating manner, an off hook relay for terminating the telephone line with a low impedance to simulate an off hook condition, a dual tone multifrequency generator to generate the dialing tones on the telephone line, a dual tone multifrequency detector to decode dual tone multifrequency tones on the telephone line or local loop, a local tone and current generator to generate current and tones on the telephone station line and a local current detector to detect current through the telephone station line.
The system, containing at least some of the above described components, provides an ordinary telephone with a large number of highly desirable operating features. Although the particular operating features performed by the system depends upon the programming of the central processing unit, the operating features can be divided into two classes - namely local operating features used by individuals on the same premises as the control system and external operating features allowing the control system to be accessed at locations remote from the premise where the control system is located.
The local operating features may include, without limitation, the ability to make and receive a phone call in a conventional manner, the ability to dial private telephone service access codes in a manner substantially faster than heretofore possible, last number redial, automatic callback even for outside lines, toll call restriction, the ability to hold incoming calls, speed dialing in which memorized numbers can be selectively dialed, local intercom-ing in which all extension telephones on the line connected to the control system ring in predetermined identifying patterns and third party conferencing in which an existing call can be placed on hold, the third party is dialed and the hold is then removed from the other party. The control system may, of course, omit one or more of the described internal operating features.
The external operating features depend on the programming of the control system at the time an incoming call is detected. The control system may be programmed in a simulated call forwarding mode in which the control system sequentially answers the incoming call, signals the telephone service to place the incoming call on hold, dials the forwarding number and then signals the phone company to release the hold. The forwarding number can also be modified from an external location by dialing the telephone station from the external location and entering an appropriate access code. The control system can also be programmed in an answering machine mode in which the message broadcast by the answering machine can be modified from an external location using an appropriate access code. The answering machine mode can be combined with the call forwarding mode to inform a caller that his call is being forwarded.
A "page alert" mode can also be implemented in combination with the answering mode either alone or with the call forwarding mode. The page alert together with the answering mode allows the answering machine to record a message from a caller and then dial a pager number to indicate that a message has been left on the answering machine. When the page alert and answering modes are combined with the call forwarding mode, the answering machine informs the incoming caller to remain on the line, the control system then dials the pager number followed by the forwarding number. This allows the individual to whom the call is being forwarded to stand by at the called station to receive the call. In a call screening mode, the control system answers incoming calls and receives screening codes dialed by the calling party. If the proper code is received, the control system will ring the telephone to which it is connected.
The control system can also be programmed to produce predetermined ringing patterns depending upon the identity of the screening code thereby identifying the caller. If the screening code is incorrect or if no screening code is dialed, no ringing occurs at the station connected to the control system, although the calling party will still hear ringing tones. The control system may also operate in a remote mode which allows a user access to the control system from an external location by dialing an appropriate access code. This remote mode allows the answering machine message to be remotely changed, it allows the call forwarding number to be remotely changed, it allows recorded speed dialing numbers to be remotely changed, and it allows calls to be made from a remote location through the telephone exchange connected to the control system. In this manner, for example, individuals may make long distance telephone calls through a public phone booth at the direct dial long distance rate. It will be understood, however, that the control system may omit one or more of the above described external features.
Still another feature of the control system allows the manufacturer of the control system to identify its customers in order to obtain an accurate customer list for receiving updated software. In accordance with this feature the control system may not be operated until the user programs the control system with his telephone number.
The control system will then automatically call the toll free number of the manufacturer and inform the manufacturer of the serial number of the control system and the phone number of the purchaser of the control system. The control system thus provides any conventional telephone station with all of the features commonly found in complex and expensive key telephone systems and PBX systems commonly found in large business organizations. Furthermore, it provides a conventional telephone with operating features that are not available on even the most complex PBX systems.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of the control system installed with a conventional desk telephone.
FIG. 2 is a block diagram of the control system of FIG. 1.
FIGS. 3a-3i form a schematic of the control system shown in block diagram form in FIG. 2.
FIGS. 4 through 38 are flow charts of the software controlling the operation of the central processing unit shown in FIGS. 2 and 3.
BEST MODE FOR CARRYING OUT THE INVENTION
The control system 10 is shown installed with a conventional desk telephone 12 in FIG. 1. The control system 10 is housed in a thin rectangular box 14 having an inclined panel 16 on which are mounted several spaced apart light emitting diodes, indicated generally at 18. The light emitting diodes 18 provide a visual indication of the operating mode or the condition of the system 10. The thin configuration of the box 14, coupled with its planar upper surface, provides a compact and inobtrusive base for the telephone 12. The control system 10 is connected to the telephone 12 through a conventional multilead conductor 20 and it is connected to a conventional telephone line through a similar multilead conductor 22. Power is supplied to the control system 10 through a conventional AC cord 24 and plug 26.
The control system 10 may be connected to any telephone line which encompasses a tip and ring type pair whether in a subscriber loop or trunk.
A block diagram of the control system 10 is illustrated in FIG. 2. The multiconductor line 22 (FIG. 1) is connected to a telephone line 22 shown in the upper left hand corner of FIG. 2 while the multiconductor line 20 (FIG. 1) connected to the telephone 12 is shown at the upper right hand corner of FIG. 2. The telephone line 22 is connected to the station line 20 through a line current detector 30 and a relay 32. The relay 3 2 is controlled by a central directly to the telephone line 22
through the line current detector 30 or to other portions of the circuitry.
The line current detector 30 measures the telephone line current in order to determine the status of the telephone line. When the line current is above a predetermined value, the line current detector 30 outputs a bit to an I/O port of the central processing unit 34.
A ring detector 33 also connected across the tip and ring lines of the telephone line detects a high voltage ring signal on those lines and outputs a logic level to an I/O port of the CPU 34. As explained in greater detail below, when a ringing signal is detected by the ring detector 33, the CPU 34 outputs a logic level from an I/O port to an off hook relay 36 that lowers the impedance between the tip and ring lines of the telephone line in order to simulate an off hook condition. Signals on the tip and ring lines are coupled to other portions of the circuitry through the off hook relay 36 and conventional audio transformer 38. These signals are received from either an external source through the telephone line 22 or through the station line 20 from the telephone 12 (FIG. 1) connected to the control system 10.
The audio signals at the output of the transformer 38 are applied to a low pass filter 40 and then to both a dual-tone multifrequency detector 42 and a band pass filter 44 The dual-tone multifrequency detector 42 decodes conventional dual tone multifrequency (DTMF) signals generated either externally or by the telephone 12. The detector 42 outputs a four bit code indicating the one of sixteen possible tone combinations corresponding to the numbers 0-9,* #, and keys A-D on some tone pads. The band pass filter 44 is centered at about 400 Hz in order to pass various supervisory tones such as busy signals The output of the band pass filter 44 is applied to a Schmitt trigger 46 whose output is applied to an I/O port of the CPU 34.
The above description deals with circuitry receiving signals from an external station through the telephone line 22 or the local station 12 through the station lines 20. The control system 10 is also capable of applying dial pulses, dual-tone multifrequency tones and supervisory tones to the telephone lines 22, or station lines 20. Accordingly, an I/O port of the CPU 34 is applied to a dial pulse generator 50 which intermittently de-energizes the off-hook relay 36 in order to momentarily raise the impedence of the telephone lines 22 to simulate dial pulses Four bits of the data bus of the CPU 34 are applied to a dual-tone multifrequency tone generator 52 which selectively generates combinations of dual tones to indicate one of 16 keys of a conventional key pad. The output of the dual tone multifrequency generator 52 is applied to the transformer 38 through an amplifier and filter 54.
The control system 10 also includes circuitry for interfacing with the local telephone 12. Accordingly, an I/O port of the CPU 34 is applied to the input of a local tone and current generator 60 that generates supervisory tones, such as busy signals, ringing signals, etc., and loop current for the telephone station 12. A local current detector 62 measures the current through the tip and ring lines 20 of the station. When the loop current rises above a predetermined value, the local current detector 62 generates an output to an I/O port of the CPU 34 to indicate an off-hook condition of the telephone station 12.
As mentioned above, the operation of the control system 10 can be divided into groups of local operating modes and external operating modes. In the local operating modes, the control system 10 is accessed through the local telephone 12 connected to the control system 10 through the station tip and ring lines 20. The local operating modes are as follows:
1. Placing a telephone call.
When the local telephone station 12 goes off hook, the telephone lines 22 are disconnected from the station 12 by energizing the relay 32. A dial tone is then applied to the local telephone station 12 by the local tone and current generator 60. The output of the dual tone multifrequency detector (DTMF) 42 and the output of the local current detector 62 are then monitored by the CPU 34 to detect dialing tones or dial pulses, respectively. The CPU 34 decodes the digits being dialed by the telephone station 12 and records these digits. If the CPU 34 determines that the station 12 is placing an outside call rather than programming the control system 10 or using the intercom function, the CPU 34 dials the recorded digits through either the dial pulse generator 50 or dual-tone multifrequency generator 52. When the CPU 34 has dialed the number of digits previously dialed by the local station 12 (i.e., the CPU 34 has "caught up" to the local station 12), the CPU 34 energizes the relay 32 to connect the telephone station tip and ring lines 20 directly to the tip and ring lines 22. Thereafter, the dial pulses or dial tones are applied by the local station 12 directly to the trunk tip and ring lines 22. The primary advantage of this "catch up" feature is the speed at which an outside number can be dialed. Conventional systems record the entire number being dialed, determine whether the number being dialed is for placing an outside call, and then apply all of the recorded numbers to the telephone lines 22. As a result, these conventional systems do not even begin applying the called number to the telephone lines 22 until after the entire called number has been dialed by the local station. In contrast, in the control system 10 when the local station completes dialing the called number, the called number has already been placed on the telephone trunk lines 22.
2. Placing a call through a private telephone service.
The "catch up" feature described above is particularly advantageous when placing a call through a private telephone service requiring a multidigit (usually seven) access code. In conventional telephone systems, one must dial the access code, wait for a dial tone, then dial a multidigit station identifier and finally the seven digit telephone number. With the control system 10, the access code digits, identifier digits, and telephone number digits are sequentially dialed without waiting for dial and other supervisory tones. The control system 10 records all of these numbers as they are dialed by the local station 12 and applies them to the telephone lines 22 in an appropriate manner. Thus, the control system 10 applies the access code digits to the telephone line, waits for a dial tone, then dials the multidigit identifier and then finally dials the seven digit telephone number. If, at any time, the control system catches up to the digits as they are being dialed by the local station
12, the CPU 34 de-energizes the relay 32 and the digits are thereafter applied to the telephone lines 22 directly from the local station. This "catch up" feature can also be used when the access code is dialed from memory Thus, a seven digit access code may be dialed from a memory location by dialing a selected digit such as "1." The caller need not wait for a supervisory tone confirming that the access code has been accepted Instead, the caller can dial the desired number immediately after dialing "1". The system will record the digits of the telephone number while the access code is being automatically dialed. After the supervisory tone confirming acceptance of the access code is received, the system automatically dials the recorded digits of the phone number and thereafter dials any remaining digits in real time as they are manually dialed It will also be understood that the telephone number may be dialed from memory instead of being dialed manually The "catch up" feature thus allows long distance telephone numbers to be dialed through a variety of long distance services in the conventional manner (i.e., "1"+area code+number").
3. Last Number Redial
The digits for each called number are decoded by either the dual-tone multifrequency detector 42 or by the CPU 34 from the output of the local current detector 62 and stored in memory. This number may be repeatedly redialed by pushing appropriate keys on the local station 12 The tones corresponding to these keys are decoded by the dual-tone multifrequency detector 42. The CPU 34 then applies dial pulses or dial tones from the dial pulse generator 50 or dual-tone multifrequency generator 52, respectively, corresponding to the memorized numbers directly to the telephone lines 22. The CPU 34 then energizes relay 32 to apply the local station 12 directly to the lines 22.
4. Automatic Call Back
In the automatic call back mode, which is entered by selecting appropriate digits on the local station key pad, a busy or unanswered line can be repeatedly called at predetermined intervals. After a call has been placed and the called station is either busy or unanswered, the automatic call back mode is selected Thereafter, the CPU 34 will apply the dial pulses through dial pulse generator 50 or dialing tones through dual-tone multifrequency generator 52 corresponding to the previously called number When and if the called party answers. The ringing or busy signal will cease, and this condition will be detected by Schmitt trigger 46, the output of which is applied to the CPU 34. The CPU 34 then causes tone generator 60 to generate a ring signal that is applied to the local station 12. When the local station 12 goes off hook, the off hook condition is detected by the local current detector 62 thereby causing the CPU 34 to energize the relay 32 and connect the local station 12 to the called party.
5. Toll Call Restriction
Local stations 12 are prevented from gaining access to the telephone lines 22 for any telephone number beginning with a "1" or "0" digit This feature is selected or overridden by dialing a four digit access code either through the local station
12 or, as explained in greater detail below, from an external station through lines 22.
6. Call Hold
Incoming calls are placed on hold by pushing the appropriate keys on the local station 12. CPU 34 then energizes the relay 32 and energizes the off hook relay 36 to maintain a low impedance condition on the lines 22. This low impedance created by the off hook relay 36 simulates the local station 12 being off hook so that the local station 12 does not hang up on the calling party. The control system 10 may be equipped with a "music on hold" feature that applies a radio station, a music synthesizer or other music to the lines 22 through the transformer 38 in the hold condition.
7. Local Intercom
By dialing an appropriate number in the local telephone 12 when the local telephone station 12 is off hook, all of the extensions to the local station can be made to ring. Moreover, the ringing pattern of the extensions can be selected by selecting appropriate digits on the local station key pad. For example, by dialing "6 N #" all of the extensions to the local station will ring in a cadance of N rings Individuals can thus be selected by selecting a ringing pattern associated with that individual. When the local intercom mode is dialed by dialing, for example "6 3 #," the CPU 34 causes the local tone and current generator 60 to place a cadance of three rings on the tip and ring line s 20 connected to the extensions of the local station 12.
The local intercom mode can also be used while an external call is placed on hold. The appropriate keys on the local station 12 are pushed, causing CPU 34 to energize relay 32 and off hook relay 36, thereby placing the outside call on hold, the CPU 34 then causes the local tone and current generator 60 to generate a dial tone for the local station 12. The local station then dials the intercom mode as described above to notify the individual corresponding to the selected cadance to pick up an extension. When the extension is picked up, the current is detected by local current detector 62. The CPU 34 then de-energizes relay 32 to connect the lines 22 to the extension of the local station 12 and de-energizes the off-hook relay 38 since the low impedance on the line 22 is now provided by the station 12 being off-hook. This provides a "call transfer" function.
8. Conferencing
In order to understand the conferencing mode, one must understand the "three-way calling" capability commonly provided by conventional telephone service. In conventional telephone service, one may join a third party in an existing telephone conversation by flashing the hook switch to hold and obtain a dial tone. The telephone number of the third party is then dialed. After the third party answers the hookswitch is once again flashed, thereby connecting all three parties to each other.
Conferencing with two outside stations can be accomplished by the control system 10 utilizing the telephone service "three-way calling" capability Accordingly, if the CPU 34 determines that the local station 12 is attempting to conference with an outside line, the off hook relay 36 is momentarily deenergized to simulate a hook flash to the telephone service central office. The existing outside call is then placed on hold thereby freeing up the lines 22 for placing another outside call. The local station 12 then dials a third party. When the third party answers, the off hook condition is detected by the line current detector 30 thereby causing the CPU 34 to actuate the off hook relay 36 to simulate a hook flash The hook flash then releases the original outside call from hold thereby connecting the two outside calls to each other and to the local station 12.
9. Memory Dialing
By selecting appropriate keys on the key pad of the local station 12, telephone numbers may be entered into memory of the CPU 34. These memorized numbers can then be selected by pressing appropriate keys on the key pad of the local station 12. The CPU 34 then dials the memorized numbers through either the dial pulse generator 50 or dual tone multifrequency generator 52. An important feature of the control system 10 is the ability to designate that the memorized numbers be dialed either through dial pulses or dialing tones. Additionally, one portion of a number can be dialed with dial pulses while the remainder is dialed through dialing tones. This is particularly important for private long distance telephone services which sometimes have an access code that can only be dialed through dial pulses. Once the long distance service has been accessed, the long distance service is capable of handling dialing tones By automatically programming the CPU 34 to dial the access code with dial pulses and the remaining digits through dialing tones, the dialing speed of the memory dialing feature can be maximized. It is also possible to link two or more memory numbers automatically so that, for example, a long distance number can be dialed followed by a delay and then the subsequent dialing of a telephone service calling number.
10. Local limited Ringing
The CPU 34 can be programmed to ring in a preselected manner although the calling party will hear a continuous ringing. In the local limited ringing mode, after a predetermined number of rings the relay 32 is energized to disconnect the local station 12 from the lines 22. At that point, the ringing signal on the lines 22 is no longer connected to the local station thereby discontinuing the ringing. If the local station 12 goes off hook, the off hook condition is detected by the local current detector 62 which causes the CPU 34 to deenergize the relay 32 thereby connecting the local station 12 to the lines 22. The CPU 34 may also be programmed to not allow the local station 12 to ring at all during certain periods. During the periods the CPU 34 energizes the relay 32 to disconnect the local station 12 from the trunk lines 22.
11. Control System Disable
The control system 10 may be effectively disabled by entering a predetermined, two digit code from the key pad of the local station 12. The CPU 34 then deenergizes the relay 32 permanently until an appropriate code is dialed so that the local station 12 is connected to the lines 22. The relay 32, of course, also connects the local station 12 to the telephone lines 22 in the event that power is lost since the lines 20 and 22 are connected to each other when the relay 32 is in the deenergized condition.
The control system also operates in a number of external modes in which the control system 10 is accessed through external stations through the lines 22. In the external operating modes, the response of the control system 10 to incoming calls depends upon the mode in which the control system is programmed. If no external modes have been programmed, the control system 10 operates in the control system disable mode in which the lines 22 are connected directly to the local station 12 The external operating modes are as follows:
1. Simulated Call Forwarding
The control system 10 utilizes the three-way calling capability of the telephone service central office in a new and different manner to perform a simulated call forwarding. In the simulated call forwarding mode, an outside call to the local station 12 is automatically routed to an external station. The ringing of the incoming call is detected by the ring detector 33 thereby causing the CPU 34 to energize the off hook relay 36 to answer the incoming call. The CPU 34 then momentarily deenergizes the off hook relay 36 to flash the central office thereby placing the incoming call on temporary hold. The CPU 34 then dials the call forwarding number either through the dial pulse generator 50 or the dual tone multifrequency generator 52. The CPU 34 then once again momentarily deenergizes the off hook relay 36 to release the held incoming call thereby connecting the incoming call to the call forwarded station. Completion of the call is detected by the line current detector 30 which causes the CPU 34 to deenergize the off hook relay 36.
The control system 10 also allows for the use of the call transfer capability of the telephone service central office, in conjunction with the simulated call forwarding method described above If this call transfer capability is available, then the control system 10 may be set to forward calls as follows The ringing of the incoming call is detected by the ring detector 33 thereby causing CPU 34 to energize the off hook relay 36 to answer the incoming call. The CPU 34 then momentarily deenergizes the off hook relay 36 to flash the central office thereby placing the incoming call on temporary hold. The CPU 34 then dials the call forwarding number either through the dial pulse generator 50, or the dual tone multi-frequency generator
52. The CPU 34 then deenergizes the off hook relay 36, causing the phone company central office to connect the incoming call directly to the call forwarded station via the central office's call transfer service, and releasing the line of the control system 10 to handle another incoming call. This significantly increases the number of calls that may be forwarded within a given period of time, since the control system is only used to set up each call.
With either method of simulated call forwarding, as described above, the control system 10 may also generate a 2 second audible ringback tone after coming off hook to answer the call, but before dailing the forwarding number. This is designed to match the normal 2 second on, 4 second off cadence of audible ringback tone, thus giving the caller confidence that the call is progressing properly.
2. Remote Programming of Call Forwarding Number
The call forwarding number is programmed or modified by first dialing a special three digit access code. This access code erases the previous call forwarding number The new call forwarding number is then dialed and stored into memory of the CPU
34. The call forwarding number can either be changed through the local station 12 or through an external station dialing the local station.
3. Answering Machine
A conventional answering machine may be connected to the control system in order to broadcast prerecorded messages and record messages from the calling party in a conventional manner. In addition to using a conventional answering machine, any information communicating device, such a voice synthesizer, tone generator or solid state voice recorder, may be used to implement this feature or any other feature described herein as using an answering machine.
4. Answering Machine and Call Forwarding
These two previously described modes can be combined to inform a calling party through the answering machine that his call is being forwarded to another number. The control system 10 then forwards the incoming call to an external location. In the answering machine and simulated call forwarding mode, the incoming call is answered by the answering machine. The current drawn by the answering machine is detected by line current detector 30 which then triggers the CPU 34. CPU 34 then starts a timer, the duration of which has been pre-programmed to be the same length as the pre-recorded message on the answering machine. When the timer expires, indicating the answering machine has broadcast the prerecorded message, the CPU 34 energizes the relay 32 which disconnects the answering machine and then energizes off hook relay 36. The CPU then momentarily deenergizes the off hook relay 36 to place the incoming call on hold. The CPU 34 then dials the forwarded number as described above before once again momentarily deenergizing the off hook relay 36 to release the hold on the calling party and connect it to the called station.
5. Page Alert
The page alert mode may be used with either the answering mode, the simulated call forwarding mode or both the answering and simulated call forwarding modes together. When used with the answering mode, an incoming call is detected by the ring detector 33 and answered by the answering machine. The answering machine then broadcasts the prerecorded message and records the message left by the calling party. When the calling party hangs up, the off hook relay 36 is energized to place the control system 10 on line. The CPU 34 then dials the telephone number of an individual's pager to signal the individual that a message has been left on his answering machine. The individual then dials the local station 12 and his call is answered by the answering machine. The individual then dials a three digit access code which prevents the control system 10 from initiating another Page Alert sequence, thus allowing the individual to retrieve the message left on the answering machine. In addition, should the caller hang up during the period in which the prerecorded message is being broadcast, the page alert function can be inhibited. This feature prevents an individual from responding to a page only to find that no message has been left on the answering machine.
In addition, when combining the page alert and answering machine modes, the control system 10 offers a special feature for display-type pagers. A display-type pager functions by having a caller dial a common phone number to reach a paging terminal. The paging terminal responds by generating a series of tones. The caller may then dial, in DTMF, a phone number that he wishes the user of the pager to call back. The paging system then transmits this number to the display of the pager and sounds an audible alert on the pager. In the past, a difficulty with this display-type paging system has been that each caller must be pre-instructed in the use of the paging system. A caller who was not instructed in its use, would not know what to do when the paging terminal responds with its tones. The control system 10 overcomes this difficulty as follows. The answering machines announcement is recorded to instruct the caller that he may dial his telephone number after the answering machines beep tone, instead of leaving a message as normal. When the caller enters his number, the digits are detected by DTMF detector 42 and stored by CPU 34. When the calling party hangs up, the off hook relay 36 is energized to place the control system 36 on line. The CPU 34 then dials the telephone number of the paging terminal, waits for detection of the response tone, then dials the number that was previously stored as entered by the caller. The off hook relay 36 is then de-energized, releasing the line, so that the next call may be handled. In this way, the control system 10 has taken the burden of dealing with the display paging terminal away from the caller, thus allowing the average, non-instructed caller to leave his telephone number for the display-type pager.
When the page alert mode is used with the simulated call forwarding mode, the incoming call is detected by the CPU 34 through the ring detector 33. The CPU 34 then energizes the off hook relay 36 to answer the incoming call. The off hook relay
36 is then momentarily deenergized to place the incoming call on hold at the central office. The CPU 34 then dials the telephone number of the pager. The CPU then momentarily deenergizes off hook relay 36 twice in succession to release the calling party from hold and to hang up on the pager. The CPU 34 then momentarily deenergizes off hook relay 36 once more, to place the calling party on hold again. The CPU 34 then dials the telephone number of the call forwarding number. The off hook relay 36
is once again momentarily deenergized to simulate a hook flash thereby releasing the calling party from the hold and connecting the calling party to the call forwarding station By dialing the pager number before dialing the call forwarding number, the individual is alerted that a call will be forwarded for him. This feature is particularly important when the individual is in a public place such as a restaurant or movie theatre because it might otherwise be difficult to locate the individual.
Finally, the page alert mode may be combined with the combination of the answering and simulated call forwarding mode. The operation in these modes is essentially as described above except that the calling party is informed by the prerecorded message on the answering machine that his call is being forwarded before the incoming call is placed on hold and the pager is dialed.
6. Call Screening
The purpose of the call screening mode is to shield the local station 12 from all incoming calls other than those dialing a predetermined call screening code. When the control system 10 is in a call screening mode, incoming calls are detected by the ring detector 33 thereby causing the CPU 34 to answer the call by energizing the off hook relay 36. The calling party then dials a predetermined access code. If the access code matches the authorized codes stored in the CPU 34, the local tone and current generator 60 generates a ringing signal on the local station 12. When the local station answers a s detected by the local current detector 62, the relay 32 is deenergized to connect the local station 12 to the calling party on the line 22. The off hook relay 36 is then deenergized. The CPU 34 can also be programmed to cause the local tone and current generator 60 to generate different ringing signals corresponding to different access codes. The ringing pattern thus identifies the calling party to allow individuals at the local station to decide whether or not they wish to answer the calling party.
7. Screening With Call Forwarding
The screening mode together with the simulated call forwarding mode is somewhat like the screening mode alone in that the identity of the calling party's access code determines the subsequent operation of the control system 10. However, instead of producing a predetermined ringing pattern corresponding to each access code, the screening with simulated call forwarding mode forwards the incoming call to one of several call forwarding numbers depending upon the identity of the access code. Thus, an incoming call is detected by the CPU 34 through the ring detector 33 and then answered by energizing the off hook relay 36. The calling party then dials the access code and the CPU 34 momentarily deenergizes the off hook relay 36 to place the calling party on hold at the central office. The CPU 34 then dials a call forwarding number corresponding to the access code through either the dial pulse generator 50 or the dual tone multifrequency generator 52. Finally, the off hook relay 36 is once again momentarily deenergized to release the hold from the calling party and connect it to the call forwarding station. The possibilities for use of the screening with simulated call forwarding mode are extensive. For example, individual employees at a business enterprise may have their own individual access numbers so that they may be individually reached by callers.
8. Screening With Simulated Call Forwarding and Answering
One limitation with the screening with simulated call forwarding mode used as described above is that individuals may not know the access code for each of the individuals that can be reached on the various call forwarding numbers. By adding the answering mode, a prerecorded message on an answering machine is broadcast after the answering machine answers the incoming call. The answering machine informs the caller of the various access codes for each individual that can be reached through the call forwarding numbers. The calling party then dials the access code for the selected individual and operation of the control system 10 proceeds as described above with reference to the screening and call forwarding mode.
9. Remote
The remote mode allows the owner access to the control system 10 by dialing an appropriate access number. This allows the individual to change call forwarding numbers, receive messages left on the answering machine, change page numbers for the page alert modes, change call screening access codes, etc., all from an external location The remote mode also allows different modes to be selected from an external location. The remote mode is accessed by dialing the local station and then dialing the predetermined access number. Although remote access to the control system 10 is described herein as being through telephone lines, it will be understood that access can also be through other communications channels, such as a radio link.
10. Money Saver
The "money saver" mode is an offshoot from the remote mode. Basically, the money saver mode allows an individual to place telephone calls from an external location, such as a telephone booth, through the local station. One of the advantages of this mode is the ability to make long distance calls from telephone booths at the direct dial rate rather than the substantially more expensive operater assisted rate required for long distance telephone calls from telephone booths. In the money saver mode, the local station is dialed and the special access number is then entered. The CPU 34 maintains the off hook relay 36 in an energized condition while the calling station dials the desired local or long distance number. The CPU then momentarily deenergizes the off hook relay 36 to simulate a hook flash thereby placing the calling station on hold at the central office. The CPU then dials the desired local or long distance number and once again momentarily deenergizes the off hook relay 36, causing the central office three-way calling service to connect the incoming call to the outgoing call. The caller may terminate this first call by dialing a terminate command. This causes the CPU to again momentarily deenergize off hook relay 36, thereby causing the central office to disconnect the other party. The caller may then dial another number if he wishes, and repeat this process as many times as desired without hanging up.
The "Money Saver" mode also may be used in conjunction with the central office call transfer service, if available. This mode functions as follows. The local station is dialed and the special access number is then entered. The CPU 34 maintains the off hook relay 36 in an energized condition while the calling station dials the desired local or long distance number. The CPU then momentarily deenergizes the off hook relay 36 to simulate a hook flash thereby placing the calling station on hold at the central office. The CPU then dials the desired local or long distance number and then deenergizes the off hook relay 36, causing the central office to connect the caller directly to the desired number via the central office's call transfer service, and thereby releasing the line of the control system 10 so that the next call may be handled. This significantly increases the number of calls that may be handled within a given period of time, since the control system is only used to set up each call rather than staying on line for the duration of each call. In this way, many users may take advantage of the same control system.
If the "Money Saver" feature is being used in the mode whereby it stays on the line for the duration of each call, then provision must be made to disconnect the call should the parties complete their call. The control system 10 employs several methods to this end. First, detection of dial tone or other supervisory signals such as busy or reorder for a predetermined time may trigger a disconnect. Second, detection of silence for a pre-determined period of time may trigger a disconnect. Third, detection of an interruption in line-current may trigger a disconnect, after the expiration of a delay designed to allow the caller time to enter a command to prevent the control system from disconnecting. This handles the situation where the other party hung up first causing a line current interruption to occur, but the original caller is still on the line and wishes to place another call through the control system. Also, the control system may be set to ignore the first interruption in line current that occurs with each call it dials. This handles the case where a line current interruption occurs when the third party answers in a three-way call. Therefore, the control system ignores the interruption that occurs when the called party answers, but accepts the interruption that occurs when either party hangs up.
The control system also employs a feature that allows the "money saver" mode to be used on a line that has central office call waiting service. The call waiting service of the central office produces a "beep" on the line if a new call is coming in while an original call is in progress. One of the parties in the original call may be placed on central office hold, while the other party speaks to the new caller. The control system handles this service as follows. An original caller may dial a second party via the control system's "money saver" feature. If, while the original caller and second party are conversing, a third party calls in attempting to use the control system, the control system will detect the call waiting signal and proceed as follows. The control system will generate a hook flash, causing the central office to place the original caller and second party on hold, allowing their conversation to continue, while connecting the new third party directly to the control system. The control system will then generate an audible busy indication to the new third party signifying the line is in use. Then the control system will hang up and wait for a ring-back from the central office indicating the original and second parties are still on central office hold. Upon detection of the ring-back, the control system will come off hook, thus taking the original party and second party off of the central office hold, reconnecting them to the control system, and restoring conditions to as they were before the call waiting signal was detected. In this way the original and second party's conversation was not interrupted yet the new third party was informed of the busy condition of the line.
One useful feature of the control system 10 is the ability to maintain an accurate and up-to-date customer list in order to provide customers with software updates resulting from newly developed features or modifications to telephone service operating perameters. Customer lists are often obtained from warranty cards which purchasers are required to return to the manufacturer to validate the warranty. The primary disadvantage of customer lists obtained in this manner, however, is the failure of many purchasers to return the warranty card. To alleviate this limitation, the CPU 34 is programmed to be inoperative until the purchaser enters his telephone number through the local station 12. Thereafter, software in the CPU 34
automatically dials the toll free number of the manufacturer and reads out the phone number of the purchaser and the serial number of the purchased unit which has also been stored in the CPU 34. This allows the manufacturer of the control system 10 to keep an accurate customer list for the sale of updated software.
It will be understood that the control system 10 may be equipped with all or only some of the above described operating features It is also apparent that other operating features may be devised which are either similar or quite different from the above described operating features Operating features can be changed at any time by merely reprogramming the CPU 34.
A schmetic for the block diagram illustrated in FIG. 2 is illustrated in FIG. 3. The CPU 34 includes a conventional microprocessor 70 driven by a conventional oscillator circuit 72 consisting of an inverter 74 having resistor 76 and the series combination of resistors 78 and crystal 80 connected in parallel from the output of inverter 74 to its input. Capacitors 82, 84, are connected from respective leads of the crystal 80 to ground. The shape of the waveform at the output of inverter 74 is restored to a clean square wave by inverter 86 before driving the microprocessor 70.
The microprocessor 70 includes "power up" circuitry 90 that resets the microprocessor 70 and other portions of the CPU 34 when power is initially applied to the system and interrupts the operation of the microprocessor 70 as power is lost from the system. When power is initially applied to the CPU 34, the +5 volt output from power supply 92 is immediately applied through resistor 94 to the RES input of the microprocessor 70. The +5 volt output of the power supply 92 is also applied through resistor 96 to the input of inverter 98. However, the input to inverter 98 is held low by capacitor 100 until capacitor 100 has charged through resistor 96. As a result, when power is initially applied to the system the input to inverter 98 is held low so that inverter 98 applies a high through resistor 102 to the base o f transistor 104. Transistor 104 then saturates causing the RESET input to microprocessor 70 to go low thereby resetting the microprocessor 70. Thus, as soon as the inverter 98 and transistor 104 receive power, the microprocessor 70 is reset by a low at the collector of transistor 104. After capacitor 100 charges through resistor 96 to the switch point of inverter 98, the output of inverter 98 goes low thereby allowing the base of transistor 104 to be held low through resistor 106. Transistor 104 is then cut off so that +5 volts is applied through resistor 94 to the RESET input of microprocessor 70. As explained in greater detail below, the power on reset is also applied to other portions of the CPU 34 as well as other circuitry in the control system 10.
When AC power to the power supply 92 is lost, the 24 vol t output of power supply 92 drops before the remaining outputs of the power supply 92 since these other outputs are more heavily filtered. The +24 volt output of the power supply 92 is applied to the cathode of Zener diode 110. The reverse biased voltage of Zener diode 110 is a fairly large percentage of +24 volts so that as the 24 volt output of the power supply 92 starts to fall, the voltage across resistor 112 quickly falls to 0
volts. However, as long as +24 volts is being applied to the Zenner diode 110, a voltage larger than about 0.7 volts is applied to the base of transistor 114 through resistor 116 thereby maintaining transistor 114 at saturation. Under these circumstances, sufficient current flows through resistor 118 so that the voltage applied to the inverting input of comparator 120 is below the threshhold voltage set by voltage divider resistors 122, 124. The positive feedback resistor 126 is connected between the output and the positive input of comparator 120 to provide hysteresis. The high at the output of comparator 120 provided through pull-up resistor 128 holds the IRQ input to the microprocessor 70 in the noninterrupted condition thereby allowing normal operation of the microprocessor 70.
When AC power is removed from the power supply 92, the voltaqe across resistor 112 quickly drops to zero thereby cutting off transistor ll4 and causing the negative in put to comparator 120 to go high. The output of comparator 120 then quickly falls to ground potential to immediately interrupt the microprocessor 70 and cause the microprocessor 70 to execute an interrupt subroutine. This interrupt subroutine terminates operation of the CPU in an orderly manner in order to prevent spurious data from being written into random access memory (RAM) as explained below The low at the output of the comparator 120 in the power down condition also discharges capacitor 100 through diode 130 and resistor 132 after the output of comparator 120 has been low for a predetermined period, capacitor 100 discharges to the switching point of inverter 98 so that inverter 98 then saturates transistor 104 and applies a negative going reset to the microprocessor 70 and other circuitry in the CPU 34 and other portions of the control system 10.
In summary, the power up circuitry 90 immediately resets the microprocessor 70 other portions of the CPU 34 and other circuitry in the control system 10 as soon as AC power is applied to the power supply 92. When AC power is removed from the power supply 92, the power up circuitry 90 immediately causes the microprocessor 70 to execute a power down interrupt subroutine and, after a short delay, resets the microprocessor 70 as well as the other circuitry in the control system that is reset upon power up of the power supply 92.
The microprocessor 70 operates in accordance with a program of instructions stored in a read only memory (ROM) 140 The ROM 140 outputs the instructions on the B0-B7 bits of an address data bus (AD BUS) from a memory location designated by the. A0-A12 address inputs. The A8-A12 bits of the address are provided by the A8-A12 bits of the microprocessor's address bus However, the address data bus B0-B7 is used as both a low order address bus and a data bus In order to allow the AD BUS to transmit instructions while the address bus is designating a location for the instructions in ROM 140, the A0-A7 bits of the address are written into an address latch 142 from the AD BUS Thus, the microprocessor 70 initially places the A0-A7 bits of the instructions address on the AD BUS and then outputs a high on its address strobe (AS) output to latch the data on the AD BUS into the address latch 142. The address latch 142 then applies the A0-A7 address bits to the ROM 140 while the A8-Al2 address bits are applied to the ROM 140 directly to the microprocessor 70. A low applied to the output enable (OE) input of the ROM 140 then outputs the instruction on the AD BUS and is read by the microprocessor 70.
The CPU 34 also includes a random access memory (RAM) 144 that is addressed in substantially the same manner as the ROM 140. However, insofar as the RAM 144 may both read and write data, a signal applied to its read (W) input designates the function of the RAM 144. The read control signal is generated as explained below Basically, a high applied to the W input causes the RAM to output data while a low applied to the W input causes the RAM 144 to input data. In either case, the RAM 144 is enabled by a low applied to its chip select (CS) input which is generated as explained below.
As mentioned above, the ROM 140 and RAM 144 are separately enabled by signals applied to their OE and CS inputs, respectively. These signals are generated by a decoding circuit from the A10-A12 address bits, R/W, data strobe (DS), a nd PA4
outputs of the microprocessor 70. The All and Al2 address bits of the microprocessor 70 are applied to NOR-gate 150 which outputs a high in the event that both address bits are low. The output of NOR-gate 150 is applied to one input of NAND-gate 152
along with the Al0 address bit of the microprocessor 70 The output of NAND-gate 152 will thus be low when the high order address bits are "100". This low at the output of NAND-gate 152 is applied to one input of NOR-gate 154 while the other input from NOR-gate 154 is connected to the PA4 output of microprocessor 70 and a manual program switch 157. Assuming that the PA4 output of microprocessor 70 is low, then independent of the state of the program switch, the output of NOR-gate 154 will be high whenever the high order address bits are "100." The high at the output of NOR-gate 154 enables NAND-gate 156 so that when a high data strobe pulse is output by the microprocessor 70, a low at the output of NAND-gate 156 generates a high at the output of inverter 158. This high at the output of inverter 158 turns on transistor 160 through resistor 162 thereby pulling sufficient current through resistor 164 to bring the chip select CS in put to RAM 144 low thereby enabling RAM 144. It is thus seen that RAM 144 will be enabled on the data strobe pulse whenever the high orders address bits are "100." The RAM 144 is disabled whenever the PA4 "external RAM disable" output is high.
A "program" switch 157 is also connected to the PA4 I/O port of microprocessor 70 through resistor 170. The PA4 port is periodically tested to detect a low caused by closing switch 157 to switch the system 10 to the programming mode. The PA4
I/O port thus serves as an input from switch 157 and as an output to NOR-gate 154.
Whenever RAM 144 is enabled by a high at the output of inverter 158, NAND-gate 172 is enabled to gate the R/W output of microprocessor 70 from inverter 174 to the read (W) input to RAM 144. Thus, if the R/W. output of microprocessor 70 is high when the RAM 144 is enabled as described above, the RAM 144 will output data on the B0-B3 bits of the AD BUS. If the R/W output of microprocessor is low, data on the B0-B3 bits of the AB BUS will be written into RAM 144 when the RAM 144 is enabled.
As mentioned above, RAM 144 is enabled only when the output of inverter 158 is high. However, a high at the output of inverter 158 can cause transistor 160 to draw sufficient current through resistor 164 to enable RAM 144 only if transistor 180
is saturated by a high applied through resistor 182 from the RESET input to microprocessor 70. Thus, when are set of the microprocessor 70 occurs by a low at the collector of transistor 104, the base of transistor 180 is pulled low through resistor 184
thereby preventing a high at the output of inverter 158 from enabling RAM 154. In short, transistor 160 and transistor 180, and their associated circuitry, function as a NAND-gate so that RAM 144 can be enabled only when microprocessor 70 is not being reset and the high order address bits are "100" during a data strobe.
In the event that the high order address bits are not "100," the output of NOR-gate 154 is low. This low at the output of NOR-gate 154 is applied to one input of NOR-gate 190. Assuming that the R/W output of microprocessor 70 is high, the output of NOR-gate 190 will be high, thereby enabling NAND-gate 192. A data strobe pulse from the DS output of microprocessor 70 will then cause NAND-gate 192 to enable the output of ROM 140. ROM 140 is thus enabled by the data strobe pulse whenever the microprocessor 70 outputs a high on the R/W output and the high order address bits are not "100."
The remaining circuitry in the CPU 34 decodes the high order address bits and the R/W output of the microprocessor 70 to provide an enable signal for the dual-tone multifrequency detector 42. Accordingly, the output of NAND-gate 156 and the output of inverter 174 are applied to NOR-gate 200. Both inputs to NOR-gate 200 are low to produce a high that enables the dual-tone multifrequency detector 42 whenever the microprocessor 70 is designating a read function by a high R/W output and the high order address bits are "100" during a data strobe pulse. Thus, when the microprocessor 70 is designating a read function, RAM 144 and dual-tone multifrequency detector 42 are simultaneously enabled. The output of RAM 144 is on the B0-B3 bits of the AD BUS and the four outputs from the dual-tone multifrequency detector 42 are on the B4-B7 bits of the AD BUS.
The ring detector 33 includes a monolithic ring detector circuit 210 having an external filter capacitor 212. The AC inputs to the monolithic ring detector circuit 212 are connected across the tip and ring lines of the telephone line 22 through resistor 214 and capacitor 216 which together implement a high pass filter. Whenever the AC voltage applied to the monolithic ring detector circuit 210 is above a predetermined value, DC current flows through resistor 218 and light emitting diode (LED)
220. Light emitting diode 220 is optically coupled to phototransistor 222 so that when LED 220 is illuminated, sufficient current is pulled through resistor 224 to apply a low to the PA7 input of microprocessor 70. The PA7 input is thus a ring detect signal that is low whenever a ringing signal is present on the telephone lines 22.
Connected across the telephone tip and ring lines 22 are a pair of back-to-back Zener diodes 226 for limiting the voltage across the tip and ring lines and a capacitor 228 for filtering very high frequency transients.
The line current detector 30; as described above with reference to FIG. 2, provides a line current detect signal responsive to the telephone line current exceeding a predetermined value. It also detects dial pulses on the telephone line. Line current is detected by a pair of light emitting diodes 230, 232 connected in series with resistor 234 and the tip line of the telephone 222. When the current flowing through the telephone tip line is below a predetermined value, relatively little illumination is emitted by the light emitting diodes 230, 232. However, as the telephone line current increases, the light emitting diodes 230, 232 emit sufficient light to saturate phototransistor 236 thereby drawing sufficient current through resistor
238 to generate a high at the output of inverter 240. This high is applied through resistor 242 to the PAl input of microprocessor 70 to indicate to the microprocessor 70 that the telephone line current is above a predetermined value. Connected in series with the telephone tip line and in parallel with resistor 234 and diodes 230, 232 are the parallel combination of three series diodes, indicated generally at 246, 248. The purpose of these diodes 246, 248 is to limit the current flowing through light emitting diodes 230, 232 to a value that will not damage the diodes 230, 232.
As is well known in the art, a n off hook condition of a telephone station is indicated by a relatively low impedance across the telephone tip and ring lines 22 Accordingly., the off hook relay 36 includes a conventional double pole relay 260
having a pair of relay contacts 262, 264 and a relay coil 266. When the relay 260 is energized by current flowing through the relay coil 266, relay contact 264 connects the tip line through dial pulse generator 50 to the ring line through transformer 38
thereby placing a relatively low impedance between the tip and ring lines. Normally, the impedance between the tip and ring lines in the on-hook condition is substantially infinite. However, operation of the control system 10 requires that signals on the telephone line 22 be received even when the telephone is on hook. For this reason, the primary of transformer 38 is connected across the tip and ring lines through resistor 270 and capacitor 272 even when the off hook relay 260 is deenergized. The relay 260 also includes a second relay contact 262 for connecting the A and A1 lines to each other in the off hook condition in the event that multiple stations are connected to the same line.
The relay 260 is energized by saturating transistor 280 thereby drawing current through the coil 266 of relay 260. The transistor 280 is saturated by a high applied through resistor 282 from the PB0 output of the microprocessor 70. The PB output of microprocessor 70 is thus an OFF HOOK RELAY signal that is high to place the control system in the off hook condition. When the off hook relay signal is low, transistor 280 is cut off by a low applied to the base of transistor 280 through resistor 284. Current flow through transistor 280 and the relay coil 260 is thus terminated Diode 286 is provided to dampen the reverse EMF spike generated across relay coil 266 when current therethrough abruptly terminates.
As mentioned above, the control system 10 is capable of dialing numbers either through dial pulses or through dual tone multifrequency signals. Dial pulses are generated by momentarily increasing the impedance between the tip and ring lines. Accordingly, the dial pulse generator 50 includes a single throw relay 290 having a single contact 292 operated by a relay coil 294. When the relay 290 is in the deenergized condition and the off hook relay 36 is in the off hook condition, contact 292
connects the tip line to the ring line through transformer 38. This connection is, of course, a relatively low impedance. When the relay 290 is momentarily deenergized thereby moving the relay contact 292 downwardly, connection between the tip and ring lines through the transformer 38 switches to the substantially higher impedance of the series combination of capacitor 296 and resistor 298.
Current flows through the coil 294 of relay 290 whenever transistor 300 is turned on by a high applied through resistor 302 from the PB1 output of microprocessor 70. The PB1 output of microprocessor 70 thus generates a DIAL PULSE BREAK signal to increase the impedance between the tip and ring lines of the telephone line 22 whenever the signal is high. When the dial pulse break signal is low, transistor 300 is held at cutoff through resistor 304 thereby terminating the flow of current through coil 294. Diode 306 is connected across relay coil 294 to dampen transients generated when current flow through the coil 294 abruptly terminates.
As mentioned above with reference to FIG. 2, a relay 32 is provided to connect the tip and ring lines 20 of the station to either the tip and ring lines of the telephone line 22 or to the control system. The relay circuit 32 includes a dual pole doubles throw relay 310 having a pair of relay contacts 312, 314 and a relay coil 316. The relay 310 is energized by turning on transistor 318 by a high applied to its base through resistor 320 from the PA0 output of microprocessor 70. The PA0 output is thus the local power relay signal which, when high, connects the telephone station lines 20 to the control system 10. When the LOCAL POWER RELAY signal is low, transistor 318 is held at cut off through resistor 322 thereby connecting the station tip and ring lines directly to the telephone tip and ring lines 22. Diode 324 is, once again, provided to dampen reverse EMF voltages generated across coil 316 when the flow of current therethrough abruptly terminates.
As mentioned earlier with reference to FIG. 2, the CPU 34 can dial utilizing a dual-tone multifrequency generator 52. The dual-tone multifrequency generator 52 consists of a conventional dual-tone multifrequency circuit 330 and a conventional shift register 332. Data designating a particular combination of dual-tone multifrequency dialing tones is loaded into the shift register 332 in a serial data stream applied to the A input of the shift register 332 from the PA6 output of the microprocessor 70. The data is clocked into the shift register 332 by a clock signal applied to the CLK input of the shift register of the 332 from the PB6 output of the microprocessor 70. When all eight bits of the shift register 332 have been loaded, the tone generator circuit 330 generates a dual-tone dialing signal corresponding to the output of the shift register 332. The dialing tone generator circuit 330 is enabled whenever a reset is not being applied to the microprocessor 70. The shift register 332 is cleared by a low applied to its CLR input whenever microprocessor 70 is being reset.
The output of the, tone generator circuit 330 is applied to an amplifier and filter 54 and the output of the amplifier and filter 54 is connected to the transformer 38. The amplifier and filter circuit includes a resistor 340 connecting the input to ground to provide a predetermined load on the dual-tone multifrequency generator 52, and a high pass network formed by resister 342 and capacitor 344 connecting the input to a summing junction of amplifier 346. A negative feedback network of the parallel combination of capacitor 348 and resistor 350 provides a low pass negative feedback network The high pass network of resistor 342 and capacitor 344 coupled with the low pass network of resistor 350 and capacitor 348 provides the operational amplifier 346 with a broad band pass characteristic encompassing the frequency range of the tones generated by the dual tone multifrequency generator 52. The gain of the operational amplifier 346 can be reduced by switching resistor 354 in parallel with resistor 350 by field effect transistor (FET) 356. The lower gain of amplifier 346 is used when a music on hold capability is employed Accordingly, when the gain is to be reduced, a low is generated at the PB6 output of microprocessor 70. This low allows transistor 360 to be held low through resistor 362. Since transistor 360 is thus a cut off, +9 volts is applied to FET 356 through resistor 364 thereby turning on FET 356 and connecting resistor 354 in parallel with resistor 350 When the PB6
output of microprocessor 70 is high, transistor 360 is turned on through resistors 366 and 368 to apply a low to the gate of FET 356 thereby removing resistor 354 from the feedback path across operational amplifier 346.
Capacitor 370 is provided to prevent transistor 360 from turning on by the clock signal applied to the clock input of shift register 332 which is also generated at the PB6 output of microprocessor 70. The output of operational amplifier 346 is applied to transformer 338 through resistor 374 and capacitor 376. The effective impedance of the amplifier and filter 54, as seen by the tip and ring lines through transformer 38, may be increased by disconnecting resistor 378 from resistor 374. Resistor 378 is connected in parallel with resistor 374 by turning on field effect transistor (FET) 380. The effective impedance of amplifier 54 must be increased in the on hook condition since, it will be remembered, the control system is connected across the tip and ring lines through resistor 270 and capacitor 272 rather than through transformer 38. In order to detect the same amplitude of signal on the tip and ring lines on the on hook condition, the impedance of amplifier 54 must be increased. Accordingly, when the off hook relay signal is low in the on hook condition, transistor 390 is cut off through resistor 392. Since transistor 390 is at cut off, the +9 volts is applied through resistor 394 and resistor 396 to the base of transistor 398
thereby causing transistor 398 to apply a low to the gate of the FET 380. This low disconnects resistor 378 from resistor 374 thereby increasing the effective impedance of the amplifier and filter 54.
Dual-tone multifrequency tones transmitted from an external location or from the local station 12 are, as explained above, coupled across the transformer 38 in either the on hook or off hook conditions, although the amplitude of the signals will be substantially higher in the off hook condition since the primary transformer 38 is then connected almost directly across the tip and ring lines. Accordingly, back-to-back Zener diodes 440 are provided to prevent excessive voltages from being generated across the secondary of the transformer 38 in the off hook condition. The signals generated across the secondary of transformer 38 are applied to the low pass filter 40 which consists of an operational amplifier 410 connected in voltage follower configuration with low pass filtering characteristics provided by resistor 412 and capacitors 414, 416. The output of amplifier 410 is biased at +9 volts through resistor 418. The output of low pass filter 40 is applied through resistor 420
and field effect transistor 422 to the summing junction of operational amplifier 424. Resistor 426 in combination with capacitor 428 sets the gain of amplifier 424 and limits the high frequency response. The output of operational amplifier 424 is applied through capacitor 430 to the input of dual-tone multifrequency detector 42. A pair of back-to-back Zener diodes 432, 434 prevent overvoltage signals from damaging dual-tone multifrequency detector 42. When enabled by a high at the output of NOR-gate 200 dual-tone multifrequency detector 42 outputs a four bit digital word on the B4-B7 bits of AD BUS indicative of the particular one of 16 keys on a key pad corresponding to the tones. Dual-tone multifrequency detector 42 also signals the microprocessor 70 of the presence of a valid tone pair by placing a high on microprocessor 70's PA5 input.
Field effect transistor 422 applies the output of low pass filter 40 to amplifier 424 when the voltage on its gate is high as explained above A high at the PB7 output of microprocessor 70 is applied through resistor 440 and resistor 442 to turn on transistor 444 thereby pulling sufficient current through resistor 446 to make the gate to FET 422 low. A high at the PB7 output of microprocessor 70 thus disconnects the output of low pass filter 40 from the dual-tone multifrequency detector 42. Capacitor 448 is provided to prevent the FET 422 from switching responsive to a clock signal which is also generated on the PB7 output of microprocessor 70.
As mentioned above, whenever the control system is in an on hook condition the PB0 ouput of microprocessor 70 is low. This low applied to transistor 390 produces a high at the collector of transistor 390 which turns on field effect transistor (FET) 450. FET 450 then switches resistor 452 parallel with resisto