Presentation on theme: "Sequential Logic Circuits. Set-Reset Latch The Set-Reset latch or bistable is a simple sequential logic circuit that remembers what has happened to the."— Presentation transcript:
Sequential Logic Circuits
Set-Reset Latch The Set-Reset latch or bistable is a simple sequential logic circuit that remembers what has happened to the inputs. If the Set is sent high or 1 then the output will be a 1 or high. The output remains high even if the Set is then sent low or 0. The output only returns to zero if the Reset is sent high or 1.
Timing Diagram The timing diagram shows the sequence in which the inputs Set and Reset must be sent high to change the output. NOTE: It is the order in which they are sent high that matters!
NOR Gate Latch The NOR gate latch circuit is a simple way of making a Set-Reset latch. You need to learn how to draw it and which input is the Set and which is the Reset. This operates in exactly the same way as the previous latch circuit.
NOR Gate Latch operation 0 0 0 0 1 1 1 0 1 0 1 At the start the Set, Reset and Q are all 0. Watch the feedback lock in the output. Now lets send the Set HIGH and see what happens. Again watch the feedback lock in the output. Now lets send the Set LOW. Make sure you can see why the output Q does NOT change. The output Q has been latched HIGH by the feedback loop. The only way to send the output Q LOW is to send the Reset HIGH. The latch has remembered that you Set the output HIGH and wont change until you tell it to Reset.