GB2030821A - Tone detector for a telephone answering system - Google Patents

Abstract

A tone detector, e.g. dial tone, for an automatic telephone answering system comprises a signal detector responsive to voice and steady tone signals for providing an indication of the status of an incoming signal on a telephone line, and a processor for monitoring line signal status to determine the presence of dial tone and to automatically disconnect the system from the telephone line. The determination of dial tone is made based upon the continuous existence, over a predetermined time interval, of an incoming line signal status representative of a steady tone signal. When the automatic telephone answering system includes a message recording system and remote access message playback a processor actuated circuitry for inserting a blank interval in an incoming tone signal prior to being recorded is provided. This prevents replayed tones from disconnecting the system from the telephone line.

Description

SPECIFICATION Telphone answering system The present invention relates to improvements in automatic telephone answering systems; and more particularly, the present invention relates to apparatus for detecting dial tone on the telephone line after the calling party hangs up, and in response thereto disconnecting from the telephone line.

At the present time there are various types of systems which automatically answer in incoming call and hold a telephone line connection which are broadly defined as "automatic Telephone Answering Systems". Included in this category of apparatus are automaic telephone message recording equipment, automatic telephone call forward equipment, automatic dial-up alarm receiving equipment, and automatic answering data entry systems. In each of these systems, some means is included for establishing a connection to the telephone line. Typically, closure of a line seizure relay is utilized to make the connection upon the occurrence of an incoming call. Disconnection from the telephone line is accomplished by opening the line seizure relay in response to a condition interpreted as a calling party hanging up.

It has been common practice in prior art automatic telephone answering systems, particularly automatic telephone message recording equipment, to control the opening of the line seizure relay with a "calling party control" (CPC) relay. The CPC relay is so interconnected with the line seizure relay that while a calling party maintains his telephone set in an "off-hook" condition, electrical current exists in the CPC relay coil and the line seizure relay maintains a connection to the telephone line. When the calling party hangs up, the CPC relay coil becomes deenergized, with resulting disconnection from the telephone line. This manner of disconnecting from the telephone line upon hang up of a calling party relies upon the detection of breaks in the subscriber loop-current.

Difficulty arises, however, with loop-current break detection of caller hang up in that apparatus is required which is capable of sensing breaks as short as 8 milliseconds. Despite the utilization of elaborate loop-current break sensing apparatus, detction of loop-current breaks and disconnection from the telephone line is frequently much later than the actual point of caller hangup at the point of switching to the central-offices "Permanent Signal" buss.

An alternative is to detect dial-tone and disconnect in response thereto. In the prior art dialtone detection has been by a tunable tone receiver added to the system. Effective dial tone detection requires a tone receiver which does not falsely indicate a dial tone detection from other line signals, such as voice signals. Thus, dial tone receivers by necessity comprise complex filter circuitry and, as a result, add measurably to the necessary system hardware.

Also, disconnection from the telephone line in response to the detection of dial tone with a tone receiver, regardless of the sophistication of the circuit design, does not provide a safeguard against inadvertent disconnection in response to transient signals appearing on the line.

Furthermore, in a message recording system having remote access message playback, dial tone detection by a tone receiver is susceptible to causing an inadvertent disconnect in response to simulated dial tone (i.e., dial tone previously recorded on the message tape and output during playback).

The present invention provides for the disconnection of automatic telephone answering system from the telephone line in response to calling party hang up as evidenced by the existence of dial tone on the telephone line.

In one aspect of the invention, following the answering of an incoming call, incoming line signal status is provided and thereafter monitored, with the answering system being automatically disconnected from the telephone line upon a determination of the presence of dial tone as the incoming line signal. The determination of dial tone is made based upon a continuous existence, over a prescribed interval, of an incoming line signal status indication representative of a steady tone.

An important feaure of this aspect of the invention is that in a message recording system the voice detection circuitry can be utilized to provide incoming line signal status.

In another aspect of the invention, a message recording system having remote access message playback can be provided with the capability to distinguish real dial tone from simulated dial tone, which exists during playback of dial tone previously recorded on the message recorder, and thereby disconnect from the telephone line only upon the existence of real dial tone.

Apparatus in accordance with the present invention for inclusion in an automatic telephone answering system having means establishing connection to a telephone line utiiizes a signal detector responsive to dial tone and information carrying line signals to provide incoming line signal status after connection is made to the telephone line and a processor for monitoring the incoming line signal status to determine the presence of dial tone based upon the existence, over a predetermined time interval, of an incoming line signal indication representative of a steady tone signal. After the presence of dial tone is determined, the line connection means is caused to automatically disconnect from the telephone line.

Further in accordance with the present invention, apparatus for inclusion in a message recording system having remote access message playback, and which disconnects upon the occurrence of dial tone, utilizes voice detection circuitry responsive to voice and dial tone signals to provide an indication of incoming line signal status. A processor monitors the line signal status during message recording to ascertain the existence, over a predetermined interval, of a status indication that a steady tone signal is the incoming line signal. In response to the existence of a steady tone status indication for a predetermined interval, processor controlled means modifies the incoming line signal by inserting a blank interval of a prescribed duration in the incoming line signal being recorded.

In the accompanying drawings: Figure 1 is a block diagram of an automatic telephone answering and message recording system in which the present invention may be incorporated; Figure 2 is a schematic diagram of circuitry for the line module portion of the system of Fig.

1; and Figure 3 is a schematic diagram of additional circuitry for the line module portion of the system of Fig. 1.

Although the present invention can be utilized in a variety of automatic telephone answering systems wherein a connection is made to the telephone line and the system is subsequently disconnected after the calling party hangs up, the presentation of the detailed description of one embodiment of the invention will be made with regard to an automatic telephone message recording system. Such equipment includes a pair of tape decks, one for recording and playing back an announcement to a calling party, and the other for recording and playing back the messages of calling parties. Control circuitry is further included for sequencing the operation of the tape recorders. Finaliy, automaic telephone answering equipment includes ring sensing and line interface circuitry.

Referring now to Fig. 1, a block diagram of an automatic telephone answering system is presented. The particular system shown is one adapted for utilization as a part of a central office automatic telephone answering system wherein a number of subscribers are connected into a central office. The system 10 includes a line module 20 connected to the central office via ring and tip lines 22, 24 and to the subscriber's telephone 30 subscriber via lines 26 and 28. A central office automatic telephone answering system comprises a number of line modules, each of which serves one subscriber. To simplify the diagram of Fig. 1, only a single line module is shown.

A processor 40 is provided to control the operation of the line module(s) 20. Processor 40 as shown comprises a microcomputer set which includes a 16-bit single-chip microprocessor. The microprocessor (MPU), for example, be a National Semiconductor IPC-16A/500D device. The micro-computer set implementing processor 40 further includes the usual associated read only memories and random access memories which communicate with the MPU over a 16-bit bidirectional bus via bidirectional bus drivers.

Processor 40 communicates with line module(s) 20 over a 1 6 bit-bidirectional bus. Address logic 50 providing STATUS STROBE and COMMAND STROBE signals to a respective line module is required for a central office telephone answering system having a plurality of subscriber line modules.

Under the direction of processor 40, line module 20 functions to sense and signal an incoming call, and transfer information between subscriber telephone 30 and message tape 60 or announce tape 70. In addition, line module 20 provides information to processor 40 relative to the operating conditions of the respective subscriber telephone answering equipment.

In Figs. 2 and 3, a subscriber's line module 20 is shown in more detail with specific electronic circuitry for implementing the module being presented.

Referring first to Fig. 2, subscriber telephone lines 26, 28 connect through resistors 102 and 104, respectively, to a resistor network 106. Subscriber telephone lines 26, 28 also connect directly to resistor network 1 06. Resistors a-d of network 106 cross-connect to provide two input lines 108, 110 to customer current detector 112, which detects on-hook and off-hook conditions on the subscriber line. An indication of the staus of the subscriber telephone 30 is transmitted via buffer 11 3 and provided to processor 40 over BUSS 1 5.

Subscriber telephone lines 26, 28 are further connected via resistors 102, 104 to the center poles of dual DPST relays 11 4A and 114B, which are actuated by relay coil 11 6. Relays 114 in the normal, de-energized state connect the subscriber telephone lines to central office ring and tip lines 22 and 24. In addition, the interconnected subscriber telephone lines and the central office lines connect to a secondary winding 11 8 of audio transformer 1 20. The circuit path of secondary winding 11 8 includes in one leg thereof a normally open relay contact 1 22 which serves as the line seizure relay for the telephone answering system.

Further connected to the ring and tip lines 22, 24 is ring detector circuitry for detecting the ringing signals for an incoming call to the subscriber's telephone 30. It will be appreciated that the incoming line signal to the subscriber is being routed through the central office of the telephone company. The ring detector comprises a differential amplifier circuit 1 24 which senses the presence of a ringing voltage between lines 22, 24. The output of amplifier 1 24 is applied via capacitor 1 26 to inverter 128, the input of which is tied to a pull-up resistor 1 30.

The output of inverter 1 28 is applied through diode 1 32 to a filter circuit comprising resistor 134, capacitor 1 36 and resistor 1 38. The output of the filter is applied via resistor 1 40 to inverting buffer 142, the output of which drives buffer 143 which supplies the ring detect (RD) signal to processor 40 via BUSS 1.

An incoming line signal over lines 22, 24 is applied to an isolation amplifier circuit 1 50. The output of isolation amplifier 1 50 is coupled via capacitor 1 52 to the input of a solid state switch 1 54. If the incoming line signal is to be passed to the automatic gain control (AGC) amplifier shown in block 156, a line record command (LRC) will condition switch 1 54 to pass the signal to resistor 1 58. The line receive command is obtained from the QB output of storage register 1 60. The data stored in register 1 60 is command information from processor 40 output over the bidirectional bus and stored in register 160 at the occurrence of a COMMAND STROBE.

The QB output of storage register 1 60 is also applied to inverter 1 62 which controls switch 1 64. With the arrangement shown, either switch 1 54 or switch 1 64 is closed and permits passage of a signal therethrough. The operation of switch 1 64 will be discussed more fully hereinafer with regard to the routing of playback signals within line module 20. Both switches 154, 164 are electronic analog CMOS switches available under the designation 401 6.

AGC amplifier 1 56 stabilizes the amplitude of the incoming line signal from isolation amplifier 1 50. Generally, AGC 1 56 comprises cascaded amplifier sections 156A, 1 56B in combination with a control element shown as a field effect transistor 1 57 which automatically changes the gain of the amplifier circuit. AGC amplifier 1 56 maintains an average output level of approximately 2.5 volts RMS despite variations in the output signal level of isolation amplifier 150.

Referring next to Fig. 3, the stabilized incoming line signal available from the AGC amplifier is made available to the message and announce tape recorders for recording of the incoming signal, and is further made available to signal detector 1 70.

In the particular embodiment illustrated, signal detector 1 70 is utilized to produce incoming line signal status indicative of the presence of an information carrying signal (i.e., voice or data) or the presence of another signal of constant frequency and amplitude (i.e., dial tone). Signal detector 1 70 in the embodiment shown provides incoming line signal status in the form of a binary signal output. For example, a fluctuating signal (such as voice) produces a pattern of "lows" and "highs" representative of binary "zeros" and "ones". A steady signal (such as dial tone) produces a continuous "low" output, that is a logic "zero". No signal at all produces a continuous ' "high".

With specific reference to the particular circuitry shown in Fig. 3 for signal detector 170, the stabilized incoming line signal from the AGC amplifier is applied to capacitor 1 72 which removes any DC component and suppresses 60 Hertz signals. Resistor 1 74 at the input of signal detector 1 70 provides a DC path to ground, and diode 1 76 rectifies the AC signal.

Resistor 1 78 and capacitor 1 80 form a "low-pass" filter with a time constant of approximately 3.9 milliseconds. A relatively short time constant in the signal detector circuit is preferable for proper voice detection Capacitor 1 80 in combination with resistor 1 82 form a discharge path with a time constant of approximately 6.8 milliseconds. Level detector 184 operates on the voltage applied to the inverting and non-inverting inputs to produce a "low" (i.e., a logic zero) output at node 1 86 when the voltage on the inverting input is more positive than the voltage on the non-inverting input. Correspondingly, level detector 184 produces a "high" (i.e., a logic one) output when the inverting input is less positive than the non-inverting input. Resistors 188, 1 90 and 1 92 provide a threshold voltage level on the non-inverting input and provide a small amount of positive feedback to provide a rapid switching action. The binary output signal is applied via resistor 1 94 to a non-inverting buffer 1 96 which drives BUSS O to provide the line signal status developed by signal detector 1 70 to processor 140. Table I below provides preferred valued for the various components of signal detector 1 70.

TABLE I Capacitor 172 .1 uf Resistor 174 4.7 K OHM Diode 176 1N4148 Resistor 178 39 K OHM Capacitor 180 .1 uf Resistor 182 68 K OHM Level Detector 1 84 LM 1458 Resistor 188 1 Meg OHM Resistor 190 10 Meg OHM Resistor 192 10 K OHM Resistor 1 94 4.7 K OHM Buffer 196 SN 7417 Proces 40 monitors incoming signal status available from signal detector 1 70 to determine the presence or absence of voice and the presence of dial tone. Because processor 40 is implemented with a microcomputer set, timing algorithms are utilized to make these determinations. It is to be understood, however, that the determinations may be made in other ways through the use of software algorithms.For example, processor 40 can be suitably implemented in random, hard-wired logic with the output of signal detector 1 70 being provided as one input thereto. In the event that hardwired logic is utilized rather than a microcomputer set, the determinations of voice, no voice and dial tone would be made using combination and sequential logic hardware in place of a software program.

Dial tone detection in accordance with the voice/dial tone detection algorithm basically involves a determination that an incoming line signal status representative to dial tone has continuously existed for a predetermined interval. In the preferred embodiment shown, if the output of signal detector 1 70 goes low and stays low for a period of six seconds, processor 40 will consider a dial tone detection to have occurred. If, however, voice detect goes low and a typical period of not less than 33 milliseconds nor more than 1 60 milliseconds exists from a previous low detect, processor 40 will consider the incoming signal to be voice. If the output of signal detector 1 70 is not changing at invervals of longer than 1 60 milliseconds to shorter than 33 milliseconds, to be voice.If the output of signal detector 1 70 is no-voice timing is started and continues until it is reset upon a determination by the processor that voice is present. If either no-voice timing reaches a prescribed duration (e.g., twelve seconds) or dial tone detection is considered to have occurred, the connection the telephone lines would be disconnected in a manner to be described later herein. Although a time interval of six seconds is preferred for making a determination of dial tone, an interval of from four to eight seconds can be successfully utilized. Program listings for the voice/dial tone detect algorithm and for the "CPC" disconnect algorithm are reproduced as Appendices A and B, respectively. It will be appreciated that the program routines are written in language for a National Semiconductor IPC-1 6A/500D microprocessor.

With continued reference to Fig. 3, the main signal path for an incoming line signal provided as the AGC amplifier output is to the message signal head, but an alternate path is to the announce signal head. To further explain, taking Fig. 2 in conjunction with Fig. 3, the AGC amplifier output signal from either a calling party or the subscriber is routed to node 200 shown in Fig. 3. If the incoming line signal is a message from a calling party to be recorded on the message tape, switch 202 is closed and the signal is coupled through capacitor 204 to the message signal head of a tape recorder. Processor 40 controls the condition of switch 202 by outputting a single-bit binary code on BUSS 1 to storage register 206.After the data bit is latched in register 206 at the occurrence of command strobe, it is made available from the 0A output of register 206 and applied via inverter 208 to a control input of switch 202.

Alternatively, if the incoming line signal is an announcement from the subscriber to be recorded on the announce tape, switch 202 is open and the signal is routed over the ANNOUNCEMENT line to switch 210 shown in Fig. 2. A record announcement command (RAC) is applied to the control input of switch 210 to cause closure thereof and make the signal at node 200 in Fig. 3 available to the announce signal head of the second tape recorder. The RAC command is obtained from processor 40 over BUSS 2. Again, the control signal available from processor 40 is a single bit binary code, the bit value of which is latched into a storage register 212 at the occurrence of command strobe and made available from the Or output of register 212.

Referring again to Fig. 3, it will be observed that the AGC amplifier output signal is routed along a signal path 214 to reach node 200. The circuitry generally designated by reference numeral 216 is preferably included in the signal path between the AGC amplifier and node 200 in an automatic telephone message recording system having remote access message playback to modify an incoming line signal if that signal produces an incoming line signal status representative of dial tone, to prevent the incoming line signal from simulating dial tone during message playback.

In the embodiment of Fig. 3, the modification to the AGC amplifier output signal is that of inserting a blank interval or "hole" of a prescribed duration. The insertion of a blank interval is accomplished in the embodiment shown by breaking the circuit path 214 and routing the AGC amplifier output signal to ground. This is accomplished in the embodiment shown with switches 218 and 220 under the direction of the processor. The AGC amplifier signal is coupled to circuit path 214 through capacitor 222 and a bias network comprising resistors 224 and 226. The signal is then conducted through resistor 228 to node 230.

Switches 218 and 220 are controlled by the same single bit binary code output by processor 40 over BUSS 5 and stored in register 206. The OB output of register 206 which makes available the control bit code is applied to an inverter 232. The output of inverter 232 is applied directly to switch 218 to control the operation thereof, and is further applied as an input to inverter 234 which provides the control signal for switch 220. It will be readily appreciated that switches 218, 220 will always be in opposite conditions; that is, when switch 218 is closed, switch 220 is open, and vice-versa.

Therefore, when switch 218 is closed, the AGC amplifier output signal is routed along circuit path 214 through resistor 236 to node 200. But when switch 218 is open, and switch 220 is closed, the AGC output signal at node 230 is routed to ground through capacitor 238.

Since the dial tone may be present for the full detection interval during recording operations, it is possible that in the caller message record mode or in the remote access announce record mode, dial tone would be recorded. In playback the recording would simulate dial tone and result in an inadvertent dial tone detection determination. To protect against an inadvertent dial tone detection determination, and permit simulated dial tone played back from tape to be distinguished from real dial tone, the processor controls switches 218 and 220 to insert a blank interval of prescribed duration into the AGC amplifier output signal. The process of inserting blank intervals in the AGC amplifier output signal may be referred to as "hole-punching".

In the preferred embodiment, hole-punching is incorporated as a part of the voice/dial tone detect algorithm. If the system is in a record mode, processor 40 monitors the output of signal detector 170, and when a steady tone is detected for a specified interval of time, a blank interval or "hole" is "punched" in the AGC amplifier output signal. So long as the steady signal appears at the input of signal detector 170, a blank interval is inserted periodically. In the preferred embodiment, the presence of a steady tone for 1.5 seconds causes a 30-millisecond blank interval to be inserted into the AGC output signal, with a blank interval being inserted every 1.5 seconds for as long as the steady signal is maintained.In playback, the 30millisecond blank intervals or holes will be utilized to reset a disconnect timer as will be more fully understood from the discussion of the overall operation of the message recording system, and the calling party disconnect procedure in particular.

Turning again to Fig. 2, playback in the system may be from either the message tape or the announcement tape. Selection of the playback source is accomplished by routing the desired source through its respective connection switch. If the message tape is selected as the playback source, switch 250 is closed and the message signal (from Fig. 3) is passed to the input of playback amplifier 254. Switch 250 is controlled by playback message comman (PMC) which is a signal derived from processor 40 via storage register 212. However, if the greeting announcement is the desired playback source, switch 250 is open and switch 252 is closed, passing the announcement signal to play back amplifier 254. Switch 252 is controlled by the playback announce command (PAC) which is also provided by processor 40 via storage register 212.

The output of playback amplifier 254 is provided via resistor 256 to switch 164, and via reistor 258 to the primary winding 260 of transformer 1 20. In normal operation with the line seizure relay 1 22 closed, the playback signal from amplifier 254 is transferred into secondary winding 11 8 and placed onto the central office lines. Further, by means of secondary winding 11 9 of transformer 120, the playback signal can be made available to the subscriber's telephone independently.

In operation, an incoming call produces a ringing voltage on the central office ring and tip lines 22, 24 which is detected by the ring detector circuitry and made available as a ring detect signal (RD) to processor 40. The processor counts the number of rings detected; and if the subscriber has not answered within a prescribed number of rings, the system will answer the incoming call. The call is answered by the processor outputting a control bit over BUSS 10 which is entered into storage register 160 upon the occurrence of COMMAND STROBE. The single bit code is output from the c output of register 1 60 and is applied to inverting relay driver 121 which energizes relay coil 123 and causes line seizure relay 122 to close.

Simultaneously, processor 40 outputs a playback announce command (PAC) to switch 252 to connect the announce tape recorder to the playback amplifier. It will, of course, be appreciated that processor 40 also provides control signals for energizing the announcement tape drive.

Following closure of relay 122, activation of the announcement tape drive, and closure of switch 210, the announcement is output via transformer 120 to the calling party.

If during the announcement the calling party hangs up, dial tone will appear on the line. In such event, dial tone mixed with the annoucement voice signal constitues the incoming line signal routed through isolation amplifier 150, switch 1 54 and AGC amplifier 1 56 to signal detector 1 70. Signal detector 1 70 responds by producing a "low" output and after six seconds of continuous dial tone the processor will determine the dial tone is present and will output a control signal to open relay 122, thereby disconnecting the system from the telephone line.

Simultaneously, of course, the announce tape drive would be rewound and set up for the next incoming call.

If the calling party remains on the line throughout the announcement portion, the system will enter the message record mode. If the calling party is leaving a message, his voice on the line will produce a voice signal as the incoming line signal. Signal detector 1 70 will respond to the voice signal as previously described. If the output of signal detector 1 70 goes "low" for a period not less than 33 milliseconds, nor more than 1 60 milliseconds following a previous "low" during a period of 1 2 seconds, processor 40 will consider the calling party to be leaving a message and maintain connection the telephone line.If, however, the output of signal detector 170 goes low and stays low for a period of 1.5 seconds, processor 40 considers that the incoming line signal is potentialy dial tone and will insert a 30 millisecond blank interval in the signal being recorded.

If the calling party hangs up during the message recording portion, the output of signal detector 1 70 goes low and stays low in response to dial tone on the line. After finding that the output of signal detector 1 70 has been continuously low for a period of six seconds, the processor will determine that dial tone is present, meaning the calling party has hung up, and the system will be disconnected from the telephone line by opening relay 1 22.

In the remote access message playback mode, a message signal from the message recorder is applied to the playback amplifier and output to the telephone line. The message signal is also provided to the AGC amplifier and output therefrom to the signal detector 1 70. If dial tone has been previously recorded on the message tape, it will be provided to the signal detector. But for the insertion of 30 milli-second blank intervals in the dial tone signal prior to it being recorded, the playback of dial tone off the message tape would cause signal detector 1 70 to produce a status indication of a steady tone signal and after six seconds the processor would react to cause disconnection of the system from the telephone line.A recorded dial tone signal having 30 millisecond blank intervals, inserted therein will when applied to signal detector 1 70 result in a "high" output signal therefrom. This detector output condition, of course, defeats the requirement in the disconnect algorithm that the incoming line status indication must be continuously low for six seconds. However, when the calling party receiving the recorded message hangs up, real dial tone comes on the line and its presence is recognized, resulting in disconnection from the telephone line.

It is also to be appreciated that during message playback, should the calling party hang up, dial tone mixed with voice signals would be passed through the isolation amplifier and AGC amplifer. The presence of dial tone, even though mixed with voice signals, still results in a low output from signal detector 1 70. Thus, following the prescribed six-second time period, the system will be disconnected from the telephone line.

The capability of signal detector 1 70 to recognize the presence of a steady dial tone signal, regardless of the frequency, even if it is mixed with voice signals, is utilized to enable the system to detect dial tone during the announcement period and during remote access message playback.

It will further be appreciated that with the present invention, apparatus for detecting dial tone can conveniently be incorporated into an automatic telephone answering system utilizing the voice detection circuitry. The dual utilization of the voice detection circuiary obviates the necessity for the inclusion of separate dial tone detection circuitry.

APPENDIX A PAGE 54 SHEP PLANTRONICS 2K SYSTEM VOICE QUERIES PAGE 'VOICE QUERIES' 2093 . LOCAL 2094 2093 , JSR QVTO 2096 , . WORD YES 2097 2098 6VTO: 2099 061C C3OB A LD RO, V12TIM(R3) 2100 061D 4502 A BOC NZ,s1 2101 sNEWVP: ; NEW VOICE PULSE, 2102 061E 1517 A JSR V121NIT 2103 061F 8001 A RTB 1 2104 , TEST FOR LEADING EDGE OF A NEW PULSE 2105 0620 CODD A sl: LD RO. NEWSTAT 2106 0621 430B A BOC ODD. sNO ; NO NEW PULSE 2107 0622 COE4 A LD RO.PRESTAT 2108 0623 4301 A BOC ODD. +2 2109 0624 190S A JMP sNO , NO NEW PLACE 2110 , YES LEADING EDGE 2111 0625 C3OA A LD RO, VPTIM(R3) 2112 0626 EOD3 A ADD RO, CLOCK 2113 0627 9447 Be JSR NCLKR1 , NEQ CLOCK TO R1 21140628 D70A A BT R1.VPTIM(R3) 2115 0629 9D9D A GKQ RO. =33 33 MILLISECONDS MIN. TIME 2116 062A 1902 A JMP sNO , NOTNEWVOICE PULSE 2117 062B 9D9C A SKO RO. = 160 ; 160 MILLISECONDS MAX. TIME 2118 062C 19F1 A JMP sNEWVP 2119 sNO: 2120 , CHECK IF 12 SECONDS ELAPSED , CHECKlF12SECONDSELAPSED 2121 062D C3OB A LD RO. V12TIM(R3) 2122 062E EOD3 A ADD RO. CLOCK 2123 062F 9D99 A SKQ RO.=TPV12 2124 0630 1901 A JMP . +2 21250631 984D Be JMP RTS1 , ,VOICE TIMED OUT 2126 0632 7001 A CAI RO. 1 2127 0633 E195 A ADD RO. =TPV12 2128 0634 9595 Ae JSR S12R 2129 0635 B001 A RTS 1 2130 2131 VOICE TIME INITIALIZE 2132 2133 V121NIT: 2134 0636 9447 Be JSR NCLKR1 2135 0637 D7OB A GT R1. V12TIM(R3) 21360638 D70A GT R1.VPTIM(R3) 2137 0639 9591 Ae JSR S12 2138 063A 2EE0 A . WORD 12000 2139 0638 8000 A RTB 2140 063C 0000 A . POOL 6 063D 0000 A 063E 0000 A 063F 0000 A 0640 0000 A 0641 0000 A 2141 APPENDIX B PAGE 64 SHEP PLANTRONICS 2K SYSTEM CPC ROUTINE PAGE 'CPC ROUTINE' 2486 .LOCAL 2487 2488 , CPCTIM: 2489 , ALL O = NOT IN CALLER MODE 2490 , BITS 2.1.0: 2491 000 TIMING FIRST 1.5 SECONDS 2492 , 001 TIMING FIRST 5. SECONDS 2493 101 TIMING FIRST 5 SECONDS BUT CPC HAS OCCURRED 2495 , X10 > 5 SECONDS NO TIMING CURRENTLY 2495 X11 > 5 SECONDS TIMING PULSE WIDTH 2496 2497 2498 QUERY CPC-IF YOU SET IDLE 2499 2500 074E C0E3 A QCPC: LD RO. PRCRAC 2501 074F 4312 A BOC NI. sRTB , < 1 MS AFTER TURNING PRC OFF 2502 0750 C304 A LD RO, LOUT(R3) 2503 0751 B80F B 8KA1 RO. =0100 2504 0752 1901 A JMP . +2 2505 0753 B000 A RTS ,PRC ON 2506 0754 C3OE A LD RO. CPCTIM(R3) 2507 0755 410C A BOC Z. sRTS 2508 2509 0756 430C A sB1X: BOC DD. sB11 2510 sB10: 2511 0757 CODD A LD RO.NEWSTAT 2512 0758 4309 A BOC ODD. sRTS , NO PULSE 2513 START START TIMING NEW CPC PULSE 2514 0759 C005 B LD RO. CPCMIN 2515 075A 9447 Be JSR NCLKR1 2516 0758 5C40 A RCPY R1, RO 2517 075C A5B6 A OR RO. = 3 , SET MODE 11 2518 075D D3OE A ET RO, CPCTIM(R3) 2519 075E 945C Be JSR RSTCPR 2520 075F C304 A LD RO. LOUT(R3) 2521 0760 4401 A BOC BTTl.sRTB ,NOT IN RECORD MODE 2522 0761 9582 Ae JSR GETCPR IN RECORD MODE AT PULSE BEGIN 2523 0762 8000 A sRTS: RTS 2524 2525 , 11 = TIMING PULSE WIDTH 2526 0763 EOD3 A sB11: ADD RO. CLOCK 2527 0764 9C05 B GKO RO.CPCMIN 2528 0765 1901 A JMP . +2 2529 0766 190E A JMP sSIDL 2530 0767 9DD4A SKO RO. =1500 2531 076B t904 A JMP s200 2532 0769 9434 Be JSR GETBIT 2533 076A ABE2 A AND RO. PHPWRD 2534 0768 4101 A BOC I. s200 2535 076C 95D0 Ae JSR BETLTC , CYCLE LTC MODE 2536 -s200: 2537 076D CODD A LD RO. NEWSTAT 2538 076E 4301 A BOC ODD. SNOPUL 2539 076F 8000 A RTS , PULSE CONTINUES APPENDIX B (cont.) PAGE 65 SHEP PANTRONICS 2K SYSTEM CPC ROUTINE 2340 STOP STOPPULSETIMING 2541 0770 5002 A sNOPUL: LI RO. 2 2542 0771 D30E A BT RO. CPCTIM(R3) 2543 0772 945C Be JSR RSTCPR 2544 0773 945D Be JSR RSTLTC 2545 0774 B000 A RTS 2546 2547 , SET IDLE 2548 sBlDL: 2549 0773 C304 A LD RO.LOUT(R3) 2550 0776 4405 A BOC BIT1. sNMR , NOT MESSAGE RECORD 2551 0777 9434 Be JSR GETBIT 2552 0778 ABD5 A AND RO. CPRWRD 2553 0779 4102 A BOC I. sNMR 2554 , MESSAGE RECORD MODE 2555 077A C5C3 A LD R1. =sBKSP ,MUST BACKSPACE OVER RECORD 2556 0778 1904 A JMP s100 2557 , GOT MESSAGE RECORD MODE 2558 sNMR: 2559 077C C43E B LD R1. =SETIDL 2560 077D 5020 A LI RO. 020 2561 077E BB06 A SKAZ RO.CODE1(R3) 2562 077F C5C4 A LD R1. =PBHGUP 2563 s100: 2564 0780 D702 A ST R1. PTR(R3) 2565 0781 6400 A PULL RO 2566 0782 99C2 Ae JMP FORCEI FORCE INTERRUPT AS STATE CHANGE 2567 2568 , INIT. CPC TIMER 2569 2570 0783 COOS B ICPC: LD RO. CPCMIN 2571 0784 4BDD A BOC N. sRTS 2572 0785 9447 Be JSR NCLKR1 2573 0786 5C40 A RCPY R1.RO 2574 0787 A9BE A AND RO. = OFFFB 2575 0788 4501 A BOC NZ. +2 2576 0789 5008 A LI RO. B 2577 078A D30E A ST R0. CPCTIM(R3) 2578 078B 945C Be JSR RSTCPR 2579 078C 8000 A RTS 2580 2581 , BACKSPACE OVER RECORD PART OF CPC TIMEOUT 2582 2583 2584 sBKSP: 2585 078D 5000 A LI RO. O 2586 078E D30E A BT RO. CPCTIM(R3) 2587 078 F 946C Be JSR BACKSP 2589 0790 0105 A . WORD 261 2589 0791 983E Be JMP SETIDL 2590 0792 0000 A . POOL 8 0793 0000 A 0794 0000 A 0795 0000 A 0796 0000 A The foregoing description of the invention has been directed to a particular preferred embodiment for purposes of explanation and illustration. It will be apparent, however, to those skilled in this art that the present invention may be utilized in an automatic telephone answering system other than an automatic telephone answering and message recording system. It is the intention of the following claims to cover all equivalent modifications and variations as fall within the scope of the invention.

Claims (21)

1. In an automatic telephone answering system, apparatus to detect dial tone on a telephone line, which comprises: a signal detector for providing an indication of the status of an incoming signal on the telephone line; and a processor for monitoring incoming line signal status to determine the presence of dial tone as the incoming line signal.

2. The apparatus of claim 1 wherein said processor detects the existence of a status indication representative of a steady tone signal over a prescribed time interval to determine the presence of dial tone.

3. The apparatus to claim 2: a. wherein said signal detector produces a binary output signal, one binary state of the output signal being assumed and maintained upon the existence of a steady tone signal as the incoming signal, and b. wherein said processor monitors the binary output signal from said signal detector to detect an uninterrupted existence of said one binary state for a prescribed duration.

4. The apparatus of claim 1, wherein said signal detector responds to an appearance of dial tone on the telephone line in the presence of voice signals on the telephone line to produce an incoming line signal status indication representative of a steady tone signal.

5. The apparatus of claim 4 wherein: said signal detector produces a binary output signal, one binary state of the output signal being assumed and maintained upon the existence of a steady tone signal on the telephone line, and the output signal alternating between binary states in response to voice signals only on the telephone line.

6. The apparatus of claim 1 wherein: said processor is a microcomputer receiviang incoming line signal status as a data input and determines the presence of dial tone utilizing a stored program routine.

7. The apparatus of claim 1 wherein: said signal detector provides incoming line signal status indications representative of steady tone signals and voice signals present on the telephone line.

8. A method of detecting dial tone on a telephone line, comprising the steps of: producing an indication of incoming line signal status; and determining the existence, over a prescribed time interval, of a status inducation representa tive of a steady tone signal.

9. The method of claim 8 wherein the prescribed time interval is four to eight seconds.

10. The method of claim 8 wherein the incoming line signal status indication produced includes a status indication representative of a steady signal, and a status indication representative of no signal.

11. The method of claim 8 wherein incoming line signal status is produced as a binary signal, one binary state of the signal being assumed and maintained upon the existence of a steady tone signal on the telephone line and the signal alternating between binary states in response to voice signals on the telephone line; and wherein the presence of dial tone is determined by detecting the uninterrupted existence over a prescribed time interval of said one binary state of the signal.

12. In an automatic telephone answering system in which a connection is made to a telephone line in response to an incoming call, the improvement comprising: a signal detector for providing an indication of the status of an incoming signal on the telephone line after a connection is made to the telephone line; a processor for monitoring incoming line signal status to determine the presence of dial tone as the incoming line signal; and processor actuated means for disconnecting from the telephone line.

1 3. The apparatus of claim 1 2 wherein said processor detects the existence, over a prescribed time interval, of a status indication representative of a steady tone signal to determine the presence of dial tone.

14. The apparatus of claim 13: a. wherein said signal detector produces a binary output signal, one binary state of the output signal being assumed and maintained upon the existence of dial tone as the incoming signal; b. wherein said processor monitors the binary output signal from said signal detector to detect an uninterrupted existence of said one binary stat for a prescribed duration; and c. wherein said processor actuated disconnecting means includes a line connection relay.

1 5. The apparatus of claim 1 2 wherein: said processor is a microcomputer receiving incoming line signal status as a data input, which determines the presence of dial tone utilizing a stored program routine.

1 6. The apparatus of claim 1 2 wherein: said processor also monitors incoming line signal status to determine the absence of a signal on the telephone line for a prescribed period of time e and in response to such determination actuates said disconnecting means.

1 7. In an automatic telephone answering and message recording system having remote access message playback capability, and including a message record tape and means for disconnecting for a telephone line in response to a detection of dial tone, the improvement comprising: a signal detector for providing an indication of the status of an incoming signal to be recorded on the message record tape; a processor for monitoring the status of the incoming signal to determine the presence of a steady tone signal; and processor actuated means for modifying the incoming signal prior to being recorded on the message record tape upon a determination by said processor that the incoming signal is a steady tone to prevent a simulation of dial tone during playback of the recorded signal and actuation of the disconnecting means.

1 8. The apparatus of claim 1 7 wherein: said processor actuated means inserts a blank interval of prescribed duration in the incoming signal to be recorded on tape.

19. The apparatus of claim 17 wherein: said processor determines the presence of a steady tone signal by detecting the existence, over a predetermined time interval, of a status indication representative thereof.

20. In an automatic telephone answering and message recording system having a remote access message playback capability, and which includes a message record tape and means for establishing a connection to a telephone line in response to an incoming call, the improvement comprising: a signal detector for providing an indication of the status of an incoming signal on the telephone line after an incoming call is answered; a processor for monitoring incoming line signal status to determine the presence of a steady tone signal as the incoming line signal and to determine the presence of dial tone as the incoming line signal; procesor actuated means for inserting a blank interval of prescribed duration in an incoming line signal prior to being recorded on the message record tape upon a determination by said processor that the incoming line signal is a steady tone signal; and processor actuated means for disconnecting said line connection means from the telephone line upon a determination by said processor that the incoming line signal is dial tone.

21. The apparatus of claim 20: a. wherein said processor detects the existence over a first predetermined time interval of a status indication representative of a steady tone signal to determine the presence of a potential dial tone signal; and b. wherein said processor detects the existence over a second predetermined time interval of a status indication representative of a steady tone signal to determine the presence of dial tone.