DATA POLARITY LATCHING SYSTEM

1,208,813. Bi-stable circuits. INTERNATIONAL BUSINESS MACHINES CORP. 30 Jan., 1968 [23 Feb., 1967], No. 4773/68. Heading H3T. A latch circuit comprises two two-state devices 11 and 12 each having two output terminals (42-45) providing a pair of complementary output signals in accordance with the state of the device, means for coupling corresponding output terminals of the circuit, means for applying binary input data at terminal 20 so as to tend to switch the devices to corresponding states, and control means 13 to prevent a change of state except when a control signal is supplied. Clock pulses are applied to terminal 21, and the output at terminal 24 follows the input data during each clock pulse and remains constant between clock pulses; a complementary output is provided at terminal 23, and a positive pulse input may be applied at terminal 22 to re-set the circuit to zero output at 23 and one output at 24. Detailed description.-When a pulse is present at terminal 21, transistors 25 and 34 are turned on. In device 11 transistors 29 and 30 are both off, and terminals 45 and 44 correspond to the input data and its complement, and these outputs appear at terminals 24 and 23. In device 12 terminal 42 is down, and transistor 37 is off so the state of the device does not affect the output at terminals 23 and 24. If the former is a one, transistor 26 is turned on so that the circuit maintains the same state when the clock pulse at 21 ceases; similarly if the output at 24 is a one, transistor 36 is turned on so that there is no change in the output when transistor 34 cuts off at the end of a clock pulse.