A latch remembers. It can be set and reset. It is a one bit memory.
Latches are useful as memory devices.
These examples also remove switch bounce.
The bounce is a mechanical problem in the switch.
Instead of switching cleanly, the switch contacts bounce and turn on and off several times, very quickly before settling.
These latches operate on the first bounce and ignore any other bounces.
Note the use of Pull-Up and Pull-Down resistors and switches on the logic inputs.
AND Latch (Debouncer)
If neither switch is pressed, if the output is high, it will stay high.
If neither switch is pressed, if the output is low, it will stay low.
If "Set" is pressed, the output will go high.
If "Reset" is pressed, the output will go low.
OR Latch (Debouncer)
If either OR gate input is high the output will be high.
If the "Set" switch is pressed, that input goes high and so does the output.
The high output is fed back to the second input so the output will stay high even if the "Set" switch is released.
To clear the latch, the "Reset" switch must be pressed. Then both inputs will be low.
When "Reset" is pressed, the output will go low and stay low when the "Reset" switch is released.
D Type Flip Flop Latch (Clock NOT Used)
Normally this chip would be clocked.
In this example the Clock and D input are not used.
The output Q can be set or reset with a high signal from the switches.
This is also a debouncing circuit.
Last Name Class ID
Q: qNum of last_q
Q ID: Question ID
Score: num correct/num attempts
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