Patent GB-681360-A (GB)
Title: Circuit arrangements for storing and retransmitting impulses
Inventor: BAKER GEORGE THOMAS
IPC: H04J3/18
Filed: 1949-06-23
Abstract: 681,360. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. May 25, 1950 [June 23, 1949], No. 16732/49. Class 40 (iv). [Also in Groups XIX and XL (c)] A storage device of the closed circulating type, i.e. one in which the stored information is regenerated by back coupling the output to the input is used in common to a number of key senders, for storing and re-transmitting digits set up thereby. As described, a cathoderay tube is used in which the impinging of the beam on an area develops a charge thereon (hereinafter called a " dot ") and thereby produces an output pulse on a pick-up plate. A beam impinging on an area already charged merely regenerates the charge but does not produce an appreciable output pulse. The screen is capable of holding 32 lines of 48 dots. 12 dots are used for each digit so that an eightdigit number occupies two lines and the tube may be common to 16 key senders. Each dot may take up one of two " positions," one vertically above the other, these positions being so close that the creation of a dot in one of the positions automatically erases a dot in the other. Normally, all the dots are in the lower position, registration of a digit n being effected by transferring the first n+1 dots to the upper position. When no writing or reading is taking place on the screen the beam, on arriving at the first area in the upper position, develops a dot and the resulting impulse is used to deflect the beam to the lower position so that the lower dot is regenerated and the recently formed upper dot is erased. The beam is maintained in the lower position until cut off preparatory to being moved to the second area where it is restored to the upper position, the process then being repeated. If a digit is to be written on the tube the deflection of the beam to the lower position is prevented while the beam scans an appropriate number of areas so that a corresponding number of dots is inserted in the upper position and the corresponding dots in the lower position erased. When such a digit is being regenerated the beam in regenerating the dots in the upper position does not produce an output pulse so that no deflection to the lower position takes place. When the digit is to be read off, the beam is caused to scan the lower position in which it creates dots and produces output pulses indicative of the stored digit. The upper position dots are thereby erased and the storage areas returned to normal. General operation, Fig. 1. A square-wave voltage from the pulse source PS switches the beam of the cathode-ray tube on and off for charging the separate areas and also pulses the stepped waveform generators XTB, and YTB, for horizontal and vertical scanning respectively. XTB also produces a " group " pulse on lead GS at the end of the scanning of the two lines necessary for recording an eight-digit number. Normally, when no writing or reading is taking place any impulses received from the pick-up plate P are fed via the " line test circuit " LTC over the lead RG to the control and discriminator circuit CD. The latter is thereby caused to effect over lead YTBA a change in the vertical scanning voltage to shift the beam from the upper to the lower position, thereby ensuring regeneration of the lower position dots. When, however, reading or writing is to take place, an " instruction " pulse is sent over the lead INS. This pulse applied to LTC diverts the memory tube output pulses from lead RG to lead TR either to set an 11-point binary counters or to saturate it according as reading or writing is taking place. In the case of writing, the beam inserts dots in the upper position until the counters, set by the key-set KS, is saturated, whereupon current is sent by S over the lead DISC to cause CD to effect the voltage shift over YTBA to move the beam to the lower position. In the case of reading, current is sent over DISC immediately to direct the beam to the lower position for production of output pulse for feeding to the counter and erasing of the dots in the upper position. The counter is then counted out by a 10 i.p.s. multi-vibrator which also transmits its pulses to line. It will be noted that the number stored on the tube is the complement with respect to 11 of the number keyed up. Detailed description. Storing the number and regeneration. Depression of one of the keys K1 ... 10, Fig. 6, operates a combination of relays KA ... KD which set up the number in binary form on the 11-point electronic counter SS1 ... 4. Relay G also comes up and transposes the " toggle " valve V18 which operates relay N and also blocks V16. Each toggle valve V14 is associated with a specific pair of lines on the screen, the valves being connected in a ring so that only one such valve is tripped at any one time, and when this is restored to normal by the group pulse GS applied over CO the next valve in the ring is tripped. The tripping of V 14 causes V15 to send an " instruction " pulse over lead INS to the control and discriminate circuit CD, Fig. 9, where it trips the toggle valve V20 cutting off the left-hand portion of V21. The line test circuit LTC is an all-electronic circuit (Fig. 5, not shown) which is represented schematically by Fig. 8 by three side-stable relays DVR, TRR, INSR whose contacts A, B are thrown into the shown positions by a pulse on their R leads and in their alternative positions by a pulse in their S leads. The " instruction pulse on INS operates INSR so that the pulse on lead AMP due to the creation of the first dot in the upper position is applied to operate TRR (DVR having been operated by the previous " twelfth pulse " over TP) whereupon subsequent pulses are diverted from lead RG to lead TR (DVR having meanwhile been restored over PS) whence they are fed via V17 (enabled by V14) to the counter SS1 ... 4. The first pulse on TR restores INSR. When the counter is counted out it sends a pulse to trip the toggle valve V18 which causes V16 to send current along lead DISC to cut off the right-hand portion of V21. This valve is now completely cut off so that V22 conducts and trips toggle valve V23 causing V25 to conduct and cut off the right-hand portion of V26. A shift voltage is thereby applied over YTBA to move the beam to the lower position where it remains, regenerating the dots in the lower position until the two lines allocated to the number have been scanned, whereupon a group pulse GS restores V20. V21 then conducts and cuts off V22, thereby allowing a " twelfth pulse " over TP to restore V23 and so shift the beam back to the upper position. TRR is restored at the end of a digit by a " twelfth pulse." During the interval between the recording of the first and second digits, the beam will normally scan the upper position and regenerate the dots therein and when no dot is encountered attempts to insert a dot. The resulting pulse, however, is fed through LTC from lead AMP to lead RG whence it is applied to trip the toggle valve V24 causing the right-hand half of V26 to conduct and move the beam to the lower position, whereby the lower dot is regenerated and the recently formed upper dot erased. V24 is restored after each dot by a pulse over PS so that the next dot is approached in the upper position and the process repeated. When a second digit is keyed up, writing takes place as described above, but on the next twelve dots. Writing cannot take place in the first twelve dots because the first dot is in the upper position so that no pulse is received over the lead AMP of LTC to operate TRR. The remainder of the digits are recorded similarly. Transmitting the number. Key KSS is operated bringing up relays IP, CL and IS. When the key is released IP and CL release, but IS holds over its slug. Valve V15 is thereby enabled to pass a pulse over lead INS when V14 is tripped, thereby tripping V20 in CD. Since V18 is normal V16 is also biased to send current over lead DISC. The circuit CD therefore operates immediately to shift the beam to the lower position, where it proceeds to insert dots and erase those in the upper position. All the resulting pulses except the first received over lead AMP are diverted as described above to the lead TR and thence to V17. The first pulse trips valve V18 to operate N which reoperates IP and holds IS. Relay IP cuts off valve V15 to prevent the transmission of a further instruction pulse over INS until the first digit has been transmitted. Relay N unblocks the multi-vibrator V19 which proceeds to apply 10 i.p.s. pulses to relay MV for outward transmission over P1, P2, and also over C6 to the counting chain SSI ... 4. When the chain is saturated, SS4 restores V18 which releases N to lock the multi-vibrator. N releases IP whose slow release period provides the inter-digital pause. When IP has released, the next time valve V14 trips a further instruction pulse is sent and V18 trips to reoperate N and IP and transmission of the next digit proceeds. If no further digit is to be transmitted, V18 does not trip and IS in due course releases to restore the circuit to normal. Cancellation of set-up digit. Operation of key KCL brings up CL which at cl5 enables V15 to send an " instruction " pulse over INS each time V14 trips. Contact cl2 maintains V18 in its normal state so that current flows over DISC to move the beam to its lower position. Contact cl3 disables the multivibrator to prevent transmission of the digits. Contact cl1 prevents the counting chain from recording pulses received over TR. The beam thus erases the dots in the upper position without any other effect.