Manual / Guide
Teletype 574-123-101TC 32 and 33 Call Control Unit - Principles of Operation
Teletype 574-123-101TC, *32 & 33 Call Control Unit — Principles of Operation* (selector magnet driver: 0.500 A from a 20 mA or 60 mA line)
Manual / Guide
Teletype 574-123-101TC, *32 & 33 Call Control Unit — Principles of Operation* (selector magnet driver: 0.500 A from a 20 mA or 60 mA line)
TELETYPE CORPORATION SECTION 574-123-101TC Skokie, Ulinois, U.S.A. Issue 2, October, 1964 @ 32 AND 33 CALL CONTROL UNIT PRINCIPLES OF OPERATION ® CONTENTS PAGE CONTENTS PAGE 1, GENERAL. ....... ea se ghee 2 3. CALL CONTROL UNIT - BELL SYSTEM SWITCHED NETWORK 2. CALL CONTROL UNIT — WESTERN A see ea a ees ee BD UNION "TELEX" SERVICE....... a OPERATION . SU eaay =| EB 3 od 2 |) | ee 3 A. General . : AG eee | 6|6 & B. Power Requirements, ee | Bg Aj SaeRerdbso sees og 3 B. Neutral Signaling Condition ... . 3 PROGRESS OF A CALL. ......... 26 C. Polar Signaling Condition. ..... 5 enaunE DISCONNECTING A CALL........ £26 POWER SUPPLY «0.6626 e eee ANSWERING ACALL,.......... 27 LOCAL-REMOTE CONTROL A. Manual Answering ...... ee ee CREATES 303 pgs gk ad ye oie ay eo Sie 6 B. Automatic Answering ........ aT A. General... . : aw a a 6 LOCAL MODE...... Peer ie hose Par are ase aT B, Proceed-to-Dial Circuit ...... 6 ‘i Pe C. Connect Cireutt 20 ee ke ws T OUT OF SERV." SWITCH........ 27 D. Local Circuit. ......, ei ae eile is] LOW-PAPER ALARM...... eee) 628 S E. Circuit Interconnections ...... 10 F. Idle Line Condition,......... ll RESTRAIN LAMP, .......+.45 ++ 2B G, Initiating aCall.......... ee TEST MODE 6 2. bc ccc eee 2p H, @onnection ...0.0 666 ce ew ae 13 L: ‘Diseonnett) O55 eo ole Se : 14 SIGNAL GENERATION .......... 29 J, Local Off-Line Operation Ha ware 14 SELECTOR MAGNET DRIVER..... 99 SELECTOR MAGNET DRIVER..... 14 A. General ..........64 eee 29 B. Circuit Description.......... 29 M LAY TIM Se ee ae ge 1 OTOR DE a 5 SPEAKER AMPLIFIER SYSTEM.... 30 POLAR ADAPTER oP ee Ge ee a ee 17 DIALER MECHANISMS a eo ere a J1 A. General ......-.2e505 reese A. Pulsing Rotary Dialer........ 31 * B. Receiving Polar Relay........ i B. Pulsing Card Dialer C. Sending Polar Relay....... oe (40A Dialer) .............. 81 DD. Connect Control Timer i ae ie oa eae 18 ce Pulsing Card Dialer E. Current Amplifier ....... eee (41A Dialer) . ae F. Circuit Interconnections ...... 21 D. TOUCH-TONE Dialer....._ ee G. Idle Line Condition. ......... 21 E, TOUCH-TONE and Card H:: Initiating: 9 Calls yieecaw coe ws 21 Dialer... 0... ccc ee uecaecace 35 I. Proceed-to-Dial,..........,. 234 J. Dialing... ......0. cee eee 24 4, CALL CONTROL UNIT— PRIVATE e K, Call Connection..,.......... 24 WIRE SERVICE........ eee 36 L. Remote Connection.......... 24 M. Call Disconnect............ 25 OPERATION .......5. aoe irs 36 N. Remote Disconnect.......... -35 O. Local Off-Line Operation. ..... 25 POWER SWITCH ........+.-.- ctae «96 © 1962 and 1964 by Teletype Corporation All rights reserved, Printed in U. 5. A, Page 1 SECTION 574-123-101 CONTENTS PAGE 5. CALL CONTROL UNIT — CIRCUIT SWITCHING SERVICE........... a6 OPERATION ..... ‘ heen: Fe A, General ..... 2.02000 220., 38 B. Idle Signal Line............ 98 C. Request Circuit ...,...0.08, 88 D. Connect Circuit..........2.. 38 E. Disconnect Circuit.......... 38 F, Remote Disconnect Circuit..... 34 G. Busy Signal,............... 38 BB: 6Doeel Circuit. cea ees we Goals 39 ANALYSIS OF CIRCUITS...... a9 A. Selector Magnet Driver....... 39 B. Motor Delay Timer.......... 39 (. Polar AGapter cae eee ee 39 D. Request Circuit...........8. 39 E. Connect Circuit... ssc. a as 40 FE: Local Cirenit. oo. Sie ee «© G, Circuit Interconnections ...... 41 H. Idle Line Condition.......... 42 I, Initiating a Call. ..... 2. ee eae 42 J. Call Connection............ 43 K, Remote Connection....... oes 43 L. Call Disconnect............ 44 M. Remote Disconnect.......... 44 N. Local Off Line Operation...... 45 1, GENERAL 1,01 This section is reissued to add coverage of the circuit switching call control unit, Since all changes are in 1,01, 1.06, and 5.01 through 5.52, marginal arrows are omitted. 1,02 The function of a call control unit is to couple a teletypewriter either to tele- graph networks or, through a data set, to tele- phone networks. In some applications, the call control unit provides facilities for initiating, accepting, controlling, and completing calls; while in others, it acts as a connecting device only, 1.03 The ecall control unit used in Western Union TELEX service operates over short and intermediate length telegraph loops using neutral signaling or over longer loops with polar signaling when modified with proper polar-to-neutral converting circuitry. It in- cludes a power supply, local-remote control circuits, a selector magnet driver circuit, and a motor delay timer circuit. Paragraphs 2.01 to 2.13 outline in general terms the call con- trol unit's overall operation. Paragraphs 2.14 Page 2 through 2.48 explain its detailed operation. The applicable schematic wiring diagram is 477T9WD. 1.04 The call control unit is used in Bell Sys- tem switched network service, Whenitis connected with the appropriate data set, it is connected with conventional telephone central offices having the required routing and message accounting equipment, These are generally the same offices and equipment serving telephone customers in the area, Direct current signals are used for both originating and terminating traffic—providing the same conditions as for conventional local telephone set operation, The dial on the call control unit, for initiation of call connections, may be either a de pulsing or a multifrequency (MF) tone device. Also included in the call control unit are ringing or tone sounding apparatus for alerting the called party. Paragraphs 3,01 through 3.06 outline in general terms the call control unit's overall operation. Paragraphs 3,08 through 3.32 explain its detailed operation, The principal applicable schematic wiring diagram is 5918WD. For additional wiring information, see the pertinent wiring diagrams, associated with the call control unit or, when provided, the appropriate section. 1,05 The eall control unit used in private wire service operates over short or inter- mediate length telegraph loops using neutral de signaling. It includes a power supply, a selector magnet driver cireuit and a power switch, Paragraphs 4,01 through 4.03 describe the call control unit generally, and paragraph 4,04 through 4,07 explain in detail its only manual control—the power switch. For wiring information see either 6353WD or 6355WD, For further wiring information see wiring diagram(s) associated with the particular call control unit or (when provided) appropriate section. 1.06 The call control unit used in a circuit switching network operates over short and intermediate length telegraph loops using neutral signaling oroverlonger loops with polar signaling when modified with proper polar-to- neutral converting circuitry. It differs from the call control unit used in Western Union TELEX service primarily in the call originating cir- cuitry. Paragraphs 5.01 through 5.10 outline the unit's overall operation. Paragraphs 5,11 through 5.52 explain its operation in detail. The applicable wiring diagrams are 7T227TWD, 7267WD, and 6481WD. Note: This unit can also be used in 35 equipment for certain circuit switching ap- plications, 2. CALL CONTROL UNIT = WESTERN UNION "TELEX" SERVICE OPERATION A. General 2,01 <A selector magnet driver circuit delivers marking signals of 0,500 ampere and spacing signals of essentially 0 ampere to the associated selector magnet. The signals trigrer the selector magnet driver circuit at about half the current level for normal (0.060 ampere mark) neutral input signals. Inteletypewriters modified for polar operation, the signal is applied to polar- to-neutral converting circuits and then to the selector magnet driver. 2.02 The operator's controls, used for orig- inating calls, consists of a set of push- button keys and a telephone-type dial: (a) There are four translucent, nonlocking pushbuttons, An illuminating lamp as- sociated with each pushbutton is energized under the operating conditions described in the following paragraphs, except that the START lamp is a spare and does not light. (b) The dial, a conventional telephone-type operates normally closed bifurcated pul- Sing contacts that open and close to send dialing pulses during the dial run-down in- terval. The pulses are produced at a rate of ten per second with the contacts open for 0,061 + 0.003 second during each pulse in- terval, A pair of normally open off-normal contacts close when the dial wheel is rotated from its idle position. These contacts pro- vide a steady mark current to "blind" the selector when dialing is undertaken. This prevents the printing of spurious characters if dialing is necessary when in the connected condition as in multi address calling, B, Neutral Signaling Condition 2.03 In the idle condition, withthe motor and typing unit stopped and visual indicators de-energized, there is a positive current of 0.005 ampere in the telegraph loop. When the calling station operator depresses the START pushbutton, it causes the shunting of a major portion of the loop resistance, and the loop current increases to 0.060 ampere, The START pushbutton must be held in the depressed posi- tion, while switching apparatus in the telegraph exchange is made available. When the circuit is ready, the telegraph exchange interrupts the ISS 2, SECTION 574-123-101 0,060 ampere loop current for about 0,025 sec- ond, This “proceed-to-dial" signal causes the DIAL lamp to be illuminated at the calling sta- tion, and it locks in the shunt to the loop resis- tance so that the operator may now release the START pushbutton and proceed to dial the num- ber of the called station. Rotation of the dial transmits signals consisting of no current for 0.06 second followed by full current (0.060 ampere) for 0.04 second during each dial pulse interval. When dialing is completed, the ex- change furnishes the connection and signifies this by reversing the telegraph loop current from positive to negative which causes the typing unit motor to start and the CONN lamp to light, Message transmission tan now be exchanged between the connected teletypwriters. The line signals are 0.060 ampere marking and zero cur- rent spacing. 2.04 If the distant called station is busy or disabled at the time ofacall, the local telegraph exchange reverses the local loopcur- rent from positive to negative for about 0.2 second and then causes it to revert to positive current again. This causes the local motor to start and the CONN lamp to light momentarily, but they then both turn off, The teletypewriter returns to the idle condition as the positive current is detected, 2.05 The local telegraph exchange responds to an incoming call by reversing the idle signal loop from positive to negative current. At the local station, the CONN lamp is illumin- ated, and the motor is turned on as the shunt to the loop resistance is applied in response to the current change. Message transmission can now take place with unattended service at the receiving station. 2.06 Following completion of traffic a dis- connect can be originated from either the calling or the called station. Holding the STOP pushbutton depressed causes the line to go open (zero current), In approximately 3 seconds the local exchange causes the con- nection to the distant station to be broken, and it reverses the current in the local loop so that positive current flows—limited by the local station loop resistance, This turns offthe motor and extinguishes the CONN lamp. The STOP pushbutton is released after the CONN lamp goes out. The original idle condition is now restored, When a disconnect is initiated from a remote station, the local exchange recognizes the open line interval and breaks the connection. The loop current is reversed back to positive, and the local station is returned to theidle con- dition as stated above. Page 3 SECTION 574-123-101 Mus 2-al TvId TVWUON dao aos YOLOW OL : c-AL OL NF dy ves a: a i y _W_ N b-PM oral 7 dl ugarsa YW | LENOWW | oy5 = ) YOLIATAS 6k et | BS cr ZI OL - | 38 oe poe aL @— YaLIUMAGALATAL | . no | ABL+ Ty a ——_+ | THONV) 6-H ) sl 7 9-18 ob 3 ANIT TVNOIS TIC FALLWOAN | Weg wok au o! Oo — >> Ten [ 8 ANI'T IWNDIS FICI FALLISOd | ot | 3 | wu = im e-a.L >|> —\ LA | ¢ | L «4 . 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If a call is received while the teletypewriter is in the local condition, the buzzer will sound for an interval of 2.6 seconds, and the teletype- writer will automatically shift over to the call- connected condition with the CONN lamp illu- minated, CC. Polar Signaling Condition 2,08 Call control units that are modified for polar operation respond to and trans- mit polar telegraph signals on separate receiv- ing and sending legs extending to the telegraph exchange facilities. The operating conditions and sequence are similar to that for neutral signaling, 2.09 In the idle condition the sending and receiving legs each have from 0.015 ta 0.040 ampere positive current flowing. The send- ing leg current is supplied by the call control unit, and the receiving leg current is supplied by the central exchange. At the local station the polar adapter interconnects the legs withthe neutral signaling control andteletypewriter cir- cuitry, Operation of the START pushbutton caus- es the current in the sending leg toreverse to a negative polarity with a value equal to the posi- tive current formerly applied (0.015 to 0.040 ampere). The telegraph exchange responds by reversing the current to negative on the re- ceiving leg for 0.025 second. This causes il- lumination of the DIAL lamp at which time the START pushbutton should be released. The dial- ing signals ¢o out over the sending leg in polar form with each pulse interval consisting of 0,06 second of positive current followed by 0.04 second of negative current. When the connec- tion is completed, the exchange reverses the polarity of the receiving leg from positive to négative current. After 0,08 second of this reversal, the call control unit causes the motor to turn on, and the CONN lampto be illuminated. Traffic can now be exchanged, Each station is arranged to record its transmitted copy. Trans- mitted and recéived signals consist of positive current for space and negative current for mark on both signal legs. ISS 2, SECTION 574-123-101 2.10 When receiving an incoming call, the local exchange reverses the receiving leg current from positive to negative, The local eall control unit, after 0,08 second of negative current, turns on the motor and the CONN licht and causes the sending leg current to be re- versed from positive to negative. 2.11 If the distant station that is called is busy, it will result in the momentary ap- plication of negative current to the local receiv- ing leg followed by areturntoacontinuous posi- tive current. The motor may run briefly, but the teletypewriter will be quickly placed back into the idle condition, 2.12 In effecting a disconnect, operation of the STOP pushbutton causes the trans- mission of positive current on the sending leg. The exchange will then reverse the current on the receiving leg to positive as it breakes con- nection to the distant station. The call control unit detects the positive current. After 1.3 sec- onds it turns the motor and CONN lamp off as it applies a steady positive current to the send- ine leg and restores the teletypewriter to the idle condition, If the disconnect is initiated at the distant teletypewriter, the positive current disconnect signal, when applied to the local receiving leg, causes the local teletypewriter to go into the idle condition after 1.3 seconds, and the sending loop becomes positive again. 2.13 For local operation the internal con- ditions are the same as for neutral signaling, Externally, the signal legs remain on positive current unless a call is received. When a call is received, a negative current on the receiving leg for 0.08 second causes the buzzer to sound for 2.6 seconds, Following the buzzer sound, teletypewriter shifts to the call-connected condition, POWER SUPPLY 2.14 Figure 1 illustrates aschematic diagram of the power input circuit. 2.15 <A fused power supply operates on 115- volts ac + 10% at 60 eps and a power in- put of 12 watts, It floats with respect to the input line; that is, it is not at earth ground. Therefore, the center tap of the transformer is t 120 volts to earth ground in neutral signaling. The polar adapter, on teletypewriters equipped for polar operation, also contains a power supply. When operating on a polar line, this power supply, as well as that of the call con- trol unit, is operated with ground to earth. Page 5 SECTION 574-123-101 LOCAL-REMOTE CONTROL CIRCUITS A. General 2,16 The local-remote control is a printed card assembly consisting of three cir- cuits that accomplish the switching called for by the input line or operation of the call con- trol unit pushbuttons. These circuits are the proceed-to-dial, connect, and local circuits. They are essentially binaries (flip-flops) that have been modified to perform their function, All the circuits are protected with a diode are suppressor against transients and voltage pul- ses generated by their associated relays. A negative voltage, generated at the collector of a transistor, will be shorted through the diode to resistor R27. The transient will be devel- oped across R27 and the lamp associated with the relay. The diodes performing this function are CR10, CR12, and CR19. The circuits are also protected from transient noise induced into them from leads in the cable to the dial and key and lamp assembly. A low-pass filter or delay network of the RC type is placed in a feedback loop in each binary. The delay net- work slows the response time of the associa- ted binary. This reduces its susceptibility to noise. These delay networks are made upof R10 and C3, R21 and C4, and R39 and C11, The sig- nal line inputs are filtered avainst spurious noise occurring on the signal line. There are two of these filters, both of the RC type. In the pro- ceed-to-dial circuit, the delay network (R5 and C1) provides 0.001 second delay, In the con- nect circuit, the delay network (R12 and C2) provides a 0.02 second delay. The RC net- work, consisting of R31 and C6, in the 240- volt signal line acts as an arc suppressor to protect associated contacts. B. Proceed-to-Ial Circuit 2.17 Figure 2 illustrates aschematic diagram of the proceed-to-dial circuit. 2.18 This circuit consists of a binary with a line input amplifier, The amplifier con- sists of transistor @1 and associated compon- ents, and the binary consists of transistors @2, Q3, and associated components, The amplifier is connected to the binary through a low-pass filter or delay network (R5 and C1) which sup- presses signal line noise. Input to the binary from the filter through R6 will turn on the pro- ceed-to-dial circuit. Two other control inputs turn off the proceed-to-dial circuit, One of these is through resistor R15, and the other is throuch Page 6 pushbutton contact 53-1. Operation of the trans- sistors in the proceed to-dial-circuit is as follows: (a) When transistor @2 is in conduction, its collector is near neutral potential, Current will flow through Q2, R11, $3-1, S3-2, and R27. Current will also flow from +18 volts through R& and CR9 to the collee- tor of Q2, The base of Q3 will be held +0.8 volt with respect to the collector of Q2 due to the current flow through CR9, The base of Q3 will, therefore, be slightly positive with respect to neutral, and 93 will be turned off, With Q3 turned off, its collector will be nega- tive, and base current to Q2 will be supplied through the low-pass filter consisting of RQ, R10, and C3 which holds 92 in conduction. (b) When transistor 93 is in conduction, the proceed-to-dial circuit is on, and the collector is near neutral. Current flows through Q3, Kl, DS-2, and R27. Since the col- lector Q3 is near neutral, current flow throuch Ri, R98, and R10 produces a positive potential at the base of Q2 which holds Q?2 off. With 2 off, base current for Q3 will flow through CR9, R11, 53-1, 83-2, and R27 holding @Q3 in conduction. (c) If an input current in excess of 0.002 ampere flows from TB-8 across CR4 to neutral, a +0.8 volt is developedacross CR4 This positive potential holds @1 inconduction and its collector near neutral potential. Neutral potential at this collector has no effect on the base of @2 because of isolation provided by R5 and R6, If the input current falls below 0,002 ampere, a -0.8 volt is developed across CR4 due to the flow of cur- rent through R43, R2, and CR4. This poten- tial turns off Q1, and its collector becomes positive, Current flows through R4 and R5 to charge Cl toward a +18 volts. When suffi- cient voltage is developed across Cl, the base of @2 will be back-biased through R6, Transistor Q2 turns off, and Q3 turns on. The proceed-to-dial circuit is now on, Back-bias to the base of @2 is supplied by the voltage divider R7, R9, and R10 so that the positive potential applied across R6 is no longer re- quired to hold Q2 off, If more than0.002 am- pere begins to flow across CRd4 again, Q1 will turn on, and its collector will go to neu- tral, but this will have no effect on the base of Q2. 18S 2, SECTION 574-123-101 TO si-2 TO 52-2 DS-LG STOP TO CONN Ds-2 q3-2 ——_——. §3-1 DIAL CN RT RB Y R4 | 22 f-- 18V 1av-J3.3K "TO CR13 yas F : Kl +18V - 18V | R5 l A s|E| sl] 2.7K Ql | & = CR10 Gla} |* CRI ole] + TO RIT 4 4 8] oa 1MFD ee qz | ci if 2 c= R10 Rg C if ca | — i Q3 bak} —r— 5. 6K 4 27 | C3 0.01 i Rl | TO R28 ? - << AN 51-47 51-5 951-6 SELECTOR START MAGNET DRIVER Figure 2 - Proceed-to-Dial Circuit (d) If negative signal is applied to the side of R15 opposite the base of @2, enough current will flow to forward-bias the base of @2 and cause it to conduct, Q3 will turn off and supply sufficient base current through RY and R10 to hold Q2 in conduction. The negative signal on R15 can now be removed, and Q2 will remain in conduction. (e) With the proceed-to-dial circuit on, Q3 in conduction, base current for Q3 flows through R1l and CR9, By operating the STOP pushbutton, the current path through Sd-1 is broken. @3 will then turn off, and Q2 will turn on, Collector current will not flaw in @2 but will be near neutral and hold Q3 off. When the STOP pushbutton is released, collector current will flow in @2. The pro- ceed-to-dial circuit is now off, C. Connect Circuit 2.19 Figure 3 illustrates aschematic diagram of the connect circuit, 2.20 This circuit consists of a binary (Q4 and 6) of which one sideis driven by emitter follower 95, The only control input to this cir- cuit is by the signal line through R12 and R13. C2 and R12 form a low-pass filter or delay net- work, Signal delay in the network is approxi- mately 0.02 second, A single passive control, consisting of R28 and CR, is used for low- paper conditions: (a) Transistor @5 controls the base of 4, If @4 is in conduction, its collector is near neutral, Voltage divider R17 and R18 hold the base of 96 positive so that ©6 is off. The Page 7 SECTION 574-123-101 TO 81-2 TO 53-1 TO 82-2 _ TO DS-LG TO LOCAL Ds-4 7) T TO DIAL % A \_/ CONN [TOCRI3. Yo ~ TO crio! _ - Ko -18V -18V +18V -18V +18V : H ; Clo} MyM) ys) Bx jp fon =/8| z{2| 8/5] <5 | R17 jro cris f ay i TO R15) | | R21 R20 Q5 S = : E | | 12K ak 10K + ss a | wh all lad CR11 ec a | | “ 4 | | CR3¥ | to} eG un | 8G ale eg | od | a) ela] BIS) els) y lasccie cot cepa eon ~__A_A_A__Aj AN TO as 4) CRE SELECTOR ~ W MAGNET DRIVER 2? —DAPER Figure 3 - Connect Circuit collector of Q6 will then be negative, and the base of @5 will be held slightly negative through R20 and R21. Since @5 is an emitter follower, its emitter will be held at the Same potential as its base. With its emitter at a negative potential, Q4 will be held on, (b) When the connect circuit is on, Q6 is in conduction, and its collector is near neutral, The voltage divider R19, R20, and R21 holds the base of @5 and therefore the emitter, positive. With the emitter of @5 positive, the base of Q4 will be back-biased, and 94 will be off. The collector of 4 will then be negative. Base current for Q6 will flow through R16 and R17 holding the connect circuit on. (c) To control the connect circuit a high voltage must be developed atthe junction of CR1 and CR2. This voltage will be approx- imately 4200 volts, If a +200 volt signal is applied at this point, the base of @5 will be biased positive, and 4 will turn off. Q6 will turn on. If a -200 volt signal is applied, the Page 8 base of Q5 will be biased negative, and Q4 will turn on. @6 will turn off, An input signal at or near neutral will have no effect upon the connect circuit, and it will remain in its prior state, (dq) The base of 5 is protected against ex- cessively high voltages by transistor operation or by CR11. If a -200 volt signal is present, the voltage on the base of 95 will fall and force its emitter to follow. When the emitter of @5 becomes negative with respect to ground, Q4 will turn on, With 4 in con- duction, its base potential is held close tothe emitter potential. Therefore, the base cannot gO more negative than approximately -0.4 volt. This action also holds the base voltare of @4 within -0.4 volt of its emitter. The base voltage of 95, then, cannot become more negative than approximately -0.8 volt. If a +200 volt signal is present at the input, the base of @5 will start to become positive. The diode CR11 is forward-biased to positive base voltages. It will limit the voltage on the base of @5 to approximately +0.8 volt. There- fore, under the severest input conditions, a voltage swing of more than +0.8 volt is not expected, (e) Resistors R24, R25, R26, and capacitor C5 are used where a polar converter is employed. As they are shown connected in 477T9WD, they have no effect on the operation of this circuit. D. Local Circuit 2.41 Figure 4 illustrates aschematic diagram of the local circuit. 2.22 A binary and a unijunction transistor timer make up the local circuit. Binary operation of Q8 and @9 is the same as that of the proceed-to-dial circuit. There are four input tontrols available, I5S 2, SECTION 574-123-101 (a) Operation of the LOCAL pushbutton turns on the local circuit (Q9 on), When con- tact 52-1 is closed, base current is supplied to @9 through R37 and R38, and Q9 will turn on. 8 will turn off, If the anode of either CR13 or CR14 is neutral, current flowing through R38 will flow through one of the diodes and not reach the base of Q9, These two diodes allow the local circuit to be turned on only when the proceed-to-dial and connect circuits are off, (o) The local circuit can be turned off by operation of either the START or the STOP pushbutton, When the local circuit is on, the base current for Q9 flows through contacts S1-1 of the START pushbutton and contact 53-1 of the STOP pushbutton. Since the contacts of the two pushbuttons are in stant /~si-2 TO 83-1 LOCAL $2-2 TO DS-LG 51-1 sa LOCAL TO CONN DS-3 - Mo MLW [ VV V VY 4 18V K3 T CR1g TO | F CR10] |, + = ; CR14 418V s) l | | of =f] [¥]s -18v | of) 2 |S e TO CR12 Ee CR1a8 — w | ot = al<le lay sy | | Qs 1 To eel | ar oF R | R39 sD CR17| C10 oe | 33K Hea. 7K Qo | | Sla)jsic 10MFD | | cit]. ool Ed fal a ial + | a 1 f R29, R300 22 3 22 ps { 4d th —~ i AL ASN TO MOTOR “ \ A DELAY TIMER TO MOTOR DELAY TIMER Figure 4 - Local Circuit Page 9 SECTION 574-123-101 series, operating either of them will turn Q9 off, (c) The unijunction transistor output will also turn off the local circuit, This transistor (Q7) is a breakdown device. If the voltage on C9 is more negative than approximately -8 volts, the resistance of the junction between the lead connected toC9and the lead connected to R35 is hich, When the voltage on C9 becomes more positive than approximately -8 volts, the resistance of this junction will become very low, and C9 will recharge through R35. The increase in cur- rent flowing through R35, while recharging C9, will cause an increase inthe voltage drop across R35. The positive pulse is coupled through C10 and CRI1T to the base of @9 and causes it to turn off and Q8 to turn on. The local circuit is then off, As capacitor C9 is recharged, the resistance of the junction again becomes high. (dq) Capacitor C9 is discharged toward neu- tral or held at about -18 volts through R32 and R33, If the input to R32 is negative (connect circuit off), the capacitor will be held at -18 volts. If the input to R32 is near neu- tral (connect circuit on), capacitor C9 will discharge through R32 and R33 toward neu- tral. At the end of 2.3 seconds interval, the voltage on C9 will be approximately -§ volts and the unijunction will break down and turn the local circuit off as described above. E. Circuit Interconnections 2.23 Figure 5 illustrates a block diagram of the local-remote control circuits. 2.24 Proceed-to-dial: (a) In order to turn on the proceed-to- dial circuit, two conditions must be sat- isfied: The START pushbutton must be opera- ted, and the proper line signal must be re- ceived from the exchange. The START push- button presents the proper signal to the exchange so that the request to dial is recognized, It also protects the proceed- to-dial circuit from an open line and long line breaks such as those penerated when the dial is operated. "LOCAL"|| "STOP" "START" PUSH- || PUSH- PUSH- BUTTON || BUTTON BUTTON ‘I | _PROCEED-TO-} ) } DIAL CIRCUIT OFF ON i - Boe: LINE 2.3-SEC |__ 4 | TIMER ; DISTRIBUTOR _ } | ee MOTOR ba, CONNECT | LINE CIRCUIT .| SENSING Ang AND bea heed = CONTROL! cer ECTOR OFF MAGNET is | is DRIVER | rte: R OFF On sh —_—— | a pe INPUTS FROM ON-OFF, PROCEED-TO-DIAL, CONNECT, AND LOCAL Figure 5 - Block Diagram of Local-Remote Control Circuits Page 10 (b) The proceed-to-dial circuit can be turned off in two ways: If the STOP pushbutton is operated or the connect circuit operates, the proceed-to-dial circuit will turn off. Local control is provided by operation of the STOP pushbutton, while the connect circuit provides automatic control initiated by the exchange. 2.29 The connect circuit is controlled only by the line and, therefore, has only one input. This input is from line sensing and con- trol as shown in Ficure 5. 2.26 Local Cireuit: (a) To turn the local circuit on, three conditions must be satisfied: (1) The proceed-to-dial and connect cir- cuits must be off. and the LOCAL pushbutton must be depressed, (2) The input of both the proceed-to-dial and the connect circuit protect against accidental operation of the local circuit which would otherwise cause anautomatic disconnect, (b) The local circuit is turned off by opera- ating the STOP pushbutton, the START pushbutton, or the 2.3-second timer. The START and STOP pushbuttons provide local control of the circuit, while the 2.3-second timer provides automatic control. The 2.3- second timer is controlled by the connect circuit which is, in turn, controlled by the line. The 2.3-second timer continues to os- cillate as long as the connect circuit is on, but only the first timing pulse is required to turn off the local circuit. (c) Each of the above three circuits has an input to the liné sensing and control, The inputs are in the form of relay contacts which switch the line through the proper inter- nal path in the local and remote control as- sembly. When either the connect or local cir- cuit is on, a motor control relay is operated. The contacts of the relay are used to turn on the motor of the associated typing unit. F,. Idle Line Condition 2.27 Figure 6 is the first of two schematic diagrams which illustrates the local- remote control circuit, It shows the current flaw during the idle line condition. ISS 2, SECTION 574-123-101 2,28 In this state all relays and lamps are off, This requires that transistors 93, Q6. and @9 be off and that Q@2, Q4, and Q8 be in con- duction, The output transistor of the motor delay timer is off, and the selector magnet driver is marking, (a) The signal loop is a 240-volt source with 4000 ohms in series. In the idle condition the local-remote control offers 43.800 ohms of local resistance to the sig- nal loop. The flow of loop current in this condition is shown in Figure 6, Current flows from TB8, the positive idle terminal. across CR4, through Rl and CR1 in parallel with the base emitter junction of Q4 and 95, R13 and R12, From this point, current flows throughthe dial pulse contacts toterm- inal TB9, (b) Loop current develops a positive po- tential at ey in Figure 6 holding transis- tor @1 on. The collector of @1 is shorted to ground through contacts 51-4 and S1-5 on the START pushbutton. Therefore, no signal is developed at the collector unless the START pushbutton is depressed, Loop cur- rent develops about -200 volts with re- spect to neutral at point . This potential holds @4 in conduction and the connect cir- cuit off (Q6 off). (e) The selector magnet driver is supplied 0.060 ampere locally to holdthe selector magnet. This current is supplied through R23 and flows through contacts “hl" and "wl," the distributor and the selector magnet driver to neutral, G. Initiating a Call 2.29 <A call can be initiated with the teletype- writer in either idle or local condition by depressing the START pushbutton. This per- forms three functions: Contacts $1-1 and 51-2 open and turn off the local circuit. Contacts 81-4 and 51-5 open and remove the short from the collector of @1, The collector will remain at ground since more than 0,002 ampere is flowing through CR4, Contacts 51-6 and 51-5 close, shorting the local loop resistance which allows the loop current to rise to 0,060 ampere. The loop current now flows from TB8, through CR4, contact 81-5, contact S1-6, CR1, and the dial impulse contacts to TB9, Shorting out the local loop resistance causes the voltage at point to rise neutral, This has no effect on the state of the connect circuit. Page 11 eee eee eee SECTION 574-123-101 +18V - 18V E SELECTOR MAGNET DRIVER OR SELECTOR MAGNET Lee DISTRIBUTOR Figure 6 - Local-Remote Control Circuit—Current Flow (Idle) (a) Proceed-to-dial: When the START push- button is depressed, a proceed-to-dial pulse will cause the collector of Q1 to go positive and, in turn, operate the proceed-to- dial circuit (turn on Q3). With Q3 in conduc- tion, current will flow through the A(K1) re- lay and the DIAL lamp. This causes both of them to be operated. The normally opencon- tact "a! of the A(K1) relay will operate the Short contacts 51-6 and S1-5 of the START pushbutton. Loop current now flows from TB8, through CR4, contact "a,"' CR1, and the dial pulse contacts to terminal TB9. (1) With @3 in conduction, its collector will be near neutral, This holds the junction of R3T and R38 in the local cir- cuit néar neutral through CR13 as the LOCAL pushbutton is depressed. The local circuit cannot now be turned on, The proceed-to-dial circuit may be turned off by operating the STOP pushbutton, Con- tacts 53-1 and 83-2 will open and cause Q3 to turn off as described earlier, With Q3 turned off the teletypewriter will revert Page 12 to the idle line condition, and the current loop will be as shown in Figure 6, (2) In initiating a call, ifthe START push- button is released at any time before the proceed-to-dial pulse is given by the exchange, the teletypewriter will revert to the idle line condition. The exchange re- quires a short time to reset after the START pushbutton is released early and should not be reoperated for a few sec- onds. (b) Dialing: The dial is in the signal loop at all times, but it may be used to transmit information to the exchange only during the proceed-to-dial and the connect conditions, Since the dial impulse contacts are in series with the loop, opera- tion of the dial will completely break loop current. In order to prevent damage to the dial contacts, an arc suppressor, R31 and C6, is placed across the contacts. +18V -18V ISS 2, SECTION 574-123-101 SELECTOR MAGNET DRIVER OR SELECTOR MAGNET i. -_ c= all Ly DISTRIBUTOR Figure 7 - Local-Remote Control Circuit—Current Flow (Local Connection) H, Connection 2,40 Figure 7 is the second of two schematic diagrams which illustrates the local- remote control circuit. It shows the current flow during local connection. 2.31 Local Connection: If a call is initiated locally, current in the loop will be 0.060 ampere from TBS to TB9 through the path described in 2.28 before connection. When the loop polarity is reversed by the exchange, current flow is from TB9 to TB8,. Diode CR1 becomes reverse-biased and stops current flow except through R12 and R13, This current flow turns off G4 and turns on the connect circuit (turns on Q6). With Q6 in conduction, the H(K2) relay will operate and the CONN lamp will light. The transfer contacts "hl" of the H{K2) relay will switch and allow loop current of 0.060 ampere to flow throughthe distributor and selec- tor magnet driver as shown in Figure 7. Loop current now flows from TB9, through the dial pulse contacts, CR2, the contacts of "hl" and “wi," the distributor, the selector magnet driver and CR4 to TBS. Current will also flow through CR15 to operate the motor delay timer and, in turn, the motor control relay M when 96 is in conduction, Contacts K4 will close and start the motor, @4 is cut off, and its collector is negative. Feedback from the collector of Q4 to the base of @2 through R15 will turn off the proceed-to-dial circuit. The A(K1) relay will release, and the DIAL lamp will go out. The "a" contact will open, but it does not have any effect upon the loop current flow, since it is not now in the current loop. The junction of R37 and R3s is held near neutral from the collector of Q6 through CR14, preventing local circuit operation. 2.32 Remote Connection: On an incoming call, the teletypewriter may be connected re- motely while in the idle line or local conditions. The loop path is shown in Figure 6 for both of these conditions, The incoming call causes the exchange to reverse the loop polarity. This causes the potential at the junction of CR1 and CR2 to change from -200 volts toapproximately +200 volts. The potential causes the connect circuit to operate as described in 2.31. Page 13 SECTION 574-123-101 2.33 Low-Paper Circuit: If the paper in a teletypewriter has become low and the low-paper contacts operate, the junction of Ri2 and R13 will not be allowed to become positive. @4 cannot be turned off, and a con- nection cannot be made, If low paper occurs dur- ing a call, the teletypewriter will remain in the connected state, since zero potential at the junction of R12 and R13 will not effect the con- nect circuit. A disconnect will occur in the normal manner, since CR3 will be back-biased to a negative potential at the junction of R12 and R13. If a eall is initiated locally with a low-paper condition, the normal sequence of events will occur until a connection is attempted. When the exchange cannot connect, it will re- verse the loop polarity, and the teletypewriter will return to the idle state, I, Disconnect 2.34 Local Disconnect: Operation of the STOP pushbutton while in the connect condition opens contacts 53-4 and 83-5, which are in series with the loop,