the ring cores. These are the Y-wire, the X-wire and the Z-wire. The Y-wire is so arranged that it passes through each core in the stack of four in one direction; the X-wire passes through each core in the stack of four at right angles to the Y-wire, and the Z-wire passes through each core in a particular waffix plane in the same direction as the X-wires (see Fig. 11). We will take as an example, the process of writing in the decimal digit 9 which, as we have already seen, is represented in the binary code by a stack of four cores magnetised in the sequence 1, 0, 0, 1.
Fig. 11 shows diagrammatically the stack of four cores, one on each of four matrix planes, which is to be brought into the conditions 1, 0, 0, 1, together with the X- and Y-wires and the four Z-wires. It should be noted that each Z- wire, one for each matrix plane, is controlled by a separate switching device.
Starting with all four of the cores concerned in the 0 condition, if current pulses equivalent to a magnetising field of +1H are passed simultaneously through the X- and Y-wires, all four cores would change to the 1 condition. But in order to write in the digit 9, it is necessary that the two centre cores shall remain in the '0' condition. This is achieved by passing at the same time a current pulse correspo~ to a field of -AH through the, Z- (or 'inhibit') wires of the two centre planes. This is shown in the diagram by the positions of the Z-switches
It will thus be clear that the top and bottom cores of the stack of four are subjected to a field of +1H by the Y-wire and a field of +1H by the X-wire, making a total of (+1H) + (-4H) = H, and will therefore change to condition 1, while the two centre cores are subjected to a field of +JH by the Y-wire, a field of +1H by the X-wire, and a field of -1H by the Z-wires, making a total of (+1/2H) + (+1H) + (-JH) = +1H only, so that they will not change from their original 0 condition.
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