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3 output SR latch

Discussion in 'General Electronics Discussion' started by rvakash, Dec 31, 2014.

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  1. rvakash


    Dec 31, 2014
    I want to build a circuit that satisfies the following truth table without using any programmable ICs. The inputs shown in the truth table are the only inputs given to the circuit and other inputs are dont care condition.

    Attached Files:

  2. Bluejets


    Oct 5, 2014
    JK flip flops perhaps...
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    If any of the inputs x, y, or z transition to 1 state, you want the associated output a, b, or c to transition to 1 state and remain there after the associated input returns to 0 state. Correct?

    What happens if more than one input transitions to the 1 state?

    How do you reset an output to 0 state after it has transitioned to 1 state?

    Simplistically, you can treat each x, y, or z input as separate logic entities, given the information provided by your "truth table".

    All that is required is three RS latches, each typically implemented as two cross-connected 2-input NOR gates. For each pair of NOR gates, the output of one NOR of the pair connects to one of the inputs of the other NOR, and the output of this NOR connects to one of the inputs of the first NOR. That is the meaning of the terminology "cross-connected" in the context of a NOR-gate implemented RS latch.

    This leaves two inputs, one on each NOR, that are used to control the set or reset state of the pair. Since you have provided no indication that a reset state is needed or wanted, one input of one NOR will be connected to logic 0 state and the other input of the other NOR will be connected to either x, y, or z. The output of the opposite NOR will be a, b, or c.

    RS latches are also available in integrated circuit packages with the cross-connections implemented internally.
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