Patent GB-878870-A (GB)
Title: Switching apparatus
IPC: G06F7/38
Filed: 1960-05-24
Abstract: 878,870. Circuits employing bi-stable magnetic elements. NATIONAL CASH REGISTER CO. May 24, 1960 [June 3, 1959], No. 18226/60. Class 40 (9). [Also in Group XIX] A bi-stable magnetic core has a continuous " 0 " state bias applied to a first winding, a " 1 " state driving pulse periodically applied to a second winding, and state "0" signals selectively applied to one or more inhibit windings, the core being switched by a power pulse to the " 1 " state only in the complete absence of inhibit signals and then returned to state " 0 " by the bias as soon as the driving pulse terminates. As shown in Fig. 1d, a core 20 is subjected to magnetizing forces-I by a bias winding Q and each of three signal windings A, B, C and a magnetizing force of + 2I is applied to a clock pulse driving winding Cw, a force of + 2I being required to reverse the magnetic state of the core when biased by - I. The arrangement is shown schematically in Fig. 1f, and if signal pulses representing the logical terms A<SP>1</SP>, B<SP>1</SP>, C<SP>1</SP> are applied, the output pulse in a sense line S1 represents the logical product A, B, C. It follows that the signal pulses represent the inverse or complement of the respective variables in a Boolean equation, and this principle is utilized in the other logical devices disclosed. Certain of the signal windings such as M, N, U, Fig. 1g, may be wound or energized in the opposite sense so as to provide an output pulse in response to the proposition LM<SP>1</SP>N<SP>1</SP>TU<SP>1</SP>X. Also two cores 20c, 20d, Fig. 2a, may be linked by a common sense line S1 and provide an output when all the windings L, M<SP>1</SP>, N or L, S, T<SP>1</SP> on respective cores are unenergized. This satisfies the Boolean equation L<SP>1</SP>MN<SP>1</SP> + L<SP>1</SP>S<SP>1</SP>T. In Fig. 2b the separate sense lines S1a, S1b of cores 20f, 20g are common to a third core 20e. This provides the logical sum of two logical products, viz. L<SP>1</SP>MN<SP>1</SP> + L<SP>1</SP>S<SP>1</SP>T on sense line S1a and the concurrent sum L<SP>1</SP>MN<SP>1</SP> + X on sense line S1b. Three separate driving windings energized by respective programme count number signals PC1, PC2, PC3 are provided on a single core 20g in Fig. 2c, each signal being obtained from a programme control core such as core Co by way of a transistor Tr and diode Di. With signal windings X<SP>1</SP>, Y<SP>1</SP>, Z<SP>1</SP>, the operation is given by the equation (PC1 + PC2 + PC3) (X, Y, Z). An adder circuit is formed in Fig. 3 by cores 50a to 50e and associated sense lines Su, Ka for the sum and carry output signals respectively. With signal input windings A, B, C and A<SP>1</SP>, B<SP>1</SP>, C<SP>1</SP> arranged on the various cores as shown, the operative equations are Su= A<SP>1</SP>B<SP>1</SP>C + A<SP>1</SP>BC<SP>1</SP> + AB<SP>1</SP>C<SP>1</SP> + ABC and Ka = A<SP>1</SP>BC + AB<SP>1</SP>C + ABC<SP>1</SP> + ABC, where A is the augend, B the addend and C the carry digit. A trigger pair BSD for use in cascaded stages is shown in Fig. 5, the true or false pulse outputs in respective sense lines 60s, 61s from cores 55, 56, 57 in a preceding stage causing a corresponding transistor 60, 61 to become conductive until such time as the other transistor is triggered to conduction. The transistor emittercollector outputs are applied by way of respective diodes 64, 65 to true and false inhibit windings 51i-54i, on cores 51-54 comprising the next state. The transistors have cross-connected base and collector electrodes in circuits which include bias potentials- 50 and + 42 and resistors R2, R3, R5-R8 across which the transient triggering conditions are developed. Such trigger pairs A, B, C are used in Fig. 4 which illustrates a binary full adder utilizing cores 51 to 56 for the logical processing and a core 57 for clearing the carry digit when required. As shown, the cores are driven by a clock pulse source 84 which also drives augend and addend signal sources 80, 81. The augend binary one and zero signals are applied over respective leads 82a, 82b to trigger pair A. Similarly the addend one and zero signals are applied over respective leads 83a, 83b to trigger pair B. The carry digit is obtained from core sense lines 60s and 61s allotted respectively to binary one and binary zero, and is registered in a trigger pair C. The trigger pair outputs are connected to winding groups A,A<SP>1</SP>: B,B<SP>1</SP>: C,C<SP>1</SP> on cores 51-56. An example is given in which the augend and addend are both binary zero and the carry digit binary one. Trigger pair outputs are then effective in windings A<SP>1</SP>, B<SP>1</SP> and C, and cores 51 and 56 only are then reversed in state by a clock pulse in winding Cw. This produces a pulse binary one output in a sum sense line Ss and a pulse in a carry zero sense line 61s, the latter causing the trigger pair C to change over to the binary zero state. To clear a carry digit, a switch " clear " is opened so that an inhibiting bias is removed from core 57. This core then changes state for the duration of the next clock pulse and induces a pulse output in the carry zero sense line 61s, thereby setting the carry digit trigger pair C to zero. The Boolean equations for this arrangement of cores and windings are: sum digit output = A<SP>1</SP>B<SP>1</SP>C<SP>1</SP> + A<SP>1</SP>BC<SP>1</SP> + AB<SP>1</SP>C<SP>1</SP> + ABC. Carry one output in sense line 60s = AB. Carry zero output in sense line 61s = A<SP>1</SP>B<SP>1</SP> + " Clear."