Patent GB-993960-A (GB)
Title: Feed-back shift register
IPC: G06F7/58
Filed: 1963-11-12
Abstract: 993,960. Circuits employing bi-stable magnetic elements. AMP Inc. Nov. 12, 1963 [Nov. 26, 1962], No. 44560/63. Heading H3B. [Also in Division G4] In a magnetic core shift register at least one pair of adjacent cores is associated with a further core which is drivable to a set state by an output signal from a succeeding stage of the register, the first core of the pair and the associated further core being arranged to be driven simultaneously towards their clear states, and being so coupled to the second core of the pair that the second core is set when one but not both of the first and further cores is driven from its set to its clear state. Each stage can operate either as a normal shift register stage or as an EXCLUSIVE-OR, or NOT, gate to which the register output can be fed back. Suggested applications are to error correction of codes and generation of pseudorandom sequences. In Fig. 1, a register is shown having three pairs of cores 2-3, 4-5, and 6-7 with further cores 13, 14, 15 and input cores 12, 1 and an output core 8. With all the cores in their clear state, apart from core 12 which is set, an advance pulse is applied to winding 18. Core 12 is then cleared and core 1 is set. After priming by energization of winding 32, and clearing by energizing winding 16, an output is produced in winding 25 to set core 2. Energization of winding 16 also resets a bi-stable circuit 20, if it was in its set condition, and this causes gate 21 to open and apply a negative potential to line 44. Thus priming winding 34 on core 2 is negatively biased, with switches 37 to 39 set as shown. Material around aperture 11 of core 3 is therefore primed, that around aperture 10 remaining unprimed, and core 13 remaining in its clear state. Winding 18 is then energized and an output pulse in winding 29 sets core 3. The registration is subsequently stepped from core 3 to core 4. With switch 38 as shown core 4 is primed by a positive bias applied from source 33, but since winding 35 is energized from the opposite end to winding 34, core 14 and material around aperture 10 remain unprimed. Registration is similarly stepped along the whole register until core 8 is set. This energizes output winding 45 to set bi-stable circuit 20, closing gate 21 and opening gate 22 to apply a positive bias to winding 44. This sets core 12 again, and the registration is then stepped as before until it reaches core 2. Since winding 44 is now positively biased the material around aperture 10 is primed and core 13 is set, while material around aperture 11 remains unprimed. When the cores are cleared the outputs induced in winding 29 by cores 2 and 13 are equal and opposite and core 3 remains unset. If core 2 had been in its clear state when winding 18 was energized then only core 13 would have been switched and core 3 would have been set. With switch 37, 38 or 39 in its " up " position a stage therefore acts as a NOT or EXCLUSIVE-OR gate. With its switch down a stage acts as a normal shift register stage. The single priming winding 44 for the even numbered cores may be replaced by separate positive and negative windings energizable by a separate source. In a modification, Fig. 2, the first core of each pair has a single outlet aperture 54, while the second core has a pair of inlet apertures 55, 56. Operation is similar, clearing from the set state of either core 48 or core 57 setting the core material around either aperture 55 or aperture 56. Clearing of both cores produces equal and opposite outputs in the transfer winding. The arrangement shown in Fig. 3 has separate transfer windings for the first core of a pair and for the further core, these windings linking opposite sides of the inlet aperture of the second core. With bi-stable circuit 96 in its reset condition no potential is applied to line 108 and a registration is passed from core to core along the register. When output core 86 is set an output in windings 107 sets bi-stable circuit 96 to apply a positive potential to line 108, thus setting cores 90 and 92. If core 84 is also in its set state when an advance pulse is applied to windings 95, cores 90, 92 and 84 are cleared and transfer windings 104, 101 and 106 are energized. Windings 101 and 106 produce additive fluxes to fully saturate core 85 in an anticlockwise direction. Priming then has no effect and no output can result, since switching in the material on both sides of aperture 88 when the core is cleared generates equal and opposite currents in the figure-eight winding. If core 84 had been in its clear state while core 92 was in its set state, clearing of both cores would set core 85. The switches in each embodiment may be electronic switches. Specification 899,366 is referred to.