Patent GB-900725-A (GB)
Title: Pulse generating circuit
IPC: G06F3/08
Filed: 1960-10-18
Abstract: 900,725. Electric selective signalling systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 18, 1960 [Nov. 3, 1959], No. 35761/60. Class 40 (1). [Also in Groups XIX, XXXIX and XL (c)] In a system in which the position of a perforation in a punched card determines the number of impulses to be transmitted by a magnetic core having two stable remanent states, the core includes a feed-back winding so that once it is set to one stable state, it commences to generate output pulses in response to a train of resetting pulses until such time as a terminating signal is applied. General arrangement.-As shown in Fig. 1, the divided input windings 81a, 81b of magnetic cores 79a, 79b are respectively energized over a brush 104a, 104b and a contact roll 106 whenever a perforation in a punched card 105 is encountered. For each possible perforation position on the card, a zeroing pulse extending over the last half of a brush pulse time period is applied to core windings 80a, 80b from a control core driver 34. Normally the cores remain in the " zero " state, but if a core is set into the " one " state it alternates between the two states in response to zeroing pulses and to " one " driving pulses fed back from an output capacitor 85a, 85b to a feed-back winding 83a, 83b. The outputs from the cores are applied from output windings 82a, 82b to respective decimal counter and carry units 19a, 17a and 19b, 17b by way of counter drivers 16a, 16b. Addition operation.-The arrangement enables two decimal numbers each represented by 'a perforation in the path of a respective brush 104a, 104b to be added, the switch 94 being closed and switch 95 opened. When a brush encounters a perforation, the associated magnetic core is switched to the one state and commences to produce output pulses under the alternate action of the control core driver and the feed-back circuit comprising capacitor 85a, resistor 86a, and inductor 87a. At the end of the card cycle cam contact 112 is closed and applies a slow-acting positive pulse to windings 80a, 80b which hold the cores at zero by preventing build-up of charge on the feed-back condensers. The output pulses produced by the respective cores are added to the count already existing in their respective counters and carry units, units from brush 104a being counted by 19a and 17a and tens from brush 104b by 19b and 17b. The carry units 17a, 17b are energized after completion of the card cycle by a pulse from a carry driver 18, and if a decimal counter has triggered its carry unit a restoring action takes place which produces an output on lead 109a or 109b. This output passes to the counter driver of the next highest order. Subtraction operation.-Switch 94 is opened, and switch 95 and a contact 115<SP>1</SP> are closed. At the commencement of a card cycle, cam contact 115 closes and applies a negative pulse to windings 80a and 80b. This sets the cores to state one, and output pulses are produced under the alternate action of the control core driver and the feed-back winding. When a brush 104a or 104b encounters a perforation, a slow-acting negative pulse is applied to winding 81a or 81b which holds the respective core in the zero state and so terminates the count. As each card column is perforated in a column position 0 to 9, the output pulses produced and counted are the nines' complement of the subtrahend, and since the minuend is already present in the counter and carry units 19a, 17a and 19b, 17b, the total count obtained is the sum of the minuend and the nines' complement. The solution is completed by an end-around-carry operation from the highest unit, and this is effected by repeated pulsing of the carry units by the carry driver 18 and connection of the highest order carry output by way of lead 109b to the counter driver 16a of lowest order. At the end of the cycle, cam contact 112 is closed to zero all the cores. Reading out.-Contact 115<SP>1</SP> is closed and a negative potential is applied to the cores at a beginning of a cycle when cam contact 115 is closed. Output pulses are then generated under the control of the core driver 34 as for the subtraetion operation, but in this case ten output pulses are produced by each core. The carry driver is also operative throughout the cycle. Each counter is therefore driven through a complete cycle and produces carry outputs in appropriate time positions at terminals 110a; 110b, the digit values being determined by timesampling these outputs. A carry pulse is not advanced to a counter of higher order as it is applied to counter driver 16b at the same time as an output pulse is received from core 79b. Time sampling.-The value of the digit readout is determined by a commutator 130, Fig. 6, the conducting arm 141 of which passes over contacts 131j to 131a in turn. Rotation of arm 141 is timed so that when drivers 18 and 34 produce their first pulse a circuit is made over contact 131j. When the second pulse is produced the circuit is made over contact 131i and so on. When an output pulse is produced by a carry unit it passes over terminal 110a to gates 147a to 147j, and one gate is opened and provides an output on lead 148a to 148j depending on the position reached by the conducting arm. Counters.-A counter 19 and carry circuit 17 is shown in detail in Fig. 2. The counter comprises counting cores 11-15 and a core 10 continuously biased to the " one " state by a winding 21. When the digit value stored is 0, the respective states of cores 11-15 are one, one, zero, zero, zero. Successive pulses from the counter driver 16 shift the one states around the counter. Each pulse from the driver 16 also temporarily reverses the state of core 10, and since windings 22 and 27 of cores 10 and 15 are in opposition a one state is established in core 11 only if core 15 is in the zero state. On the tenth pulse core 11 is in state one and core 12 in state zero. A one is inserted in a carry core 17<SP>1</SP> on transfer of the states of cores 12 and 11 to cores 13 to 12, since no inhibiting signal is present in the winding of 17<SP>1</SP> connected between the latter cores. The change of state of core 17<SP>1</SP> produces an output in winding 33. Drivers.-The counter drivers 16a, 16b each comprise a self-extinguishing thyratron circuit, Fig. 3, having input firing terminals 46 and 49 respectively connected to a control core and to the carry output from the preceding stage. When the thyratron 35 is fired, its anode potential falls to an extent which allows capacitor 38 to discharge and produce an output pulse over terminal 36. A coil 39 limits the current buildup and extends the pulse width. When the thyratron cuts off due to reduction of anode voltage the capacitor recharges. The control core driver, Fig. 4, uses a similar circuit but has only one input which is connected by a relay contact 60 to either cam contact 61 or 63.