Flip Flops – Notes – 1

1. A flip-flop is a logic circuit with a memory characteristic such that its Q and ar{Q} outputs will go to a new state in response to an input pulse and will remain in that new state after the input pulse is terminated.

2. A NAND latch and a NOR latch are simple FFs that respond to logic levels on their SET and RESET inputs.

3. Clearing (resetting) a FF means that its output ends up in the Q=0/ar{Q}=1 state. Setting a FF means that it ends up in the Q=1/ar{Q}=0 state.

4. Clocked FFs have a clock input (CLK, CP, CK) that is edge-triggered, meaning that it triggers the FF on a positive-going transition (PGT) or a negative-going transition (NGT).

5. Edge-triggered (clocked) FFs can be triggered to a new state by the active edge of the clock input according to the state of the FF’s synchronous control inputs (S,R or J, K or D).

6. Most clocked FFs also have asynchronous inputs that can set or clear the FF independently of the clock input.

7. The D latch is a modified NAND latch that operates like a D flip-flop except that it is not edge-triggered.

8. Some of the principal uses of FFs include data storage and transfer, data shifting, counting, and frequency division. They are used in sequential circuits that follow a predetermined sequence of states.

9. A one-shot (OS) is a logic circuit that can be triggered from its normal resting state ( Q=0) to its triggered state ( Q=1 ), where it remains for a time interval proportional to an RC time constant.

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