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 AS Level     Logic     Algebra     >Bistable Latch<     Karnaugh Maps     Multiplexing     NOR Array     Propagation Delay

# Logic Bistable Latch

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AS Level    Combinational Logic    Questions 0 to 26   -->  View All

## Bistable Latch (Debouncer)

Also known as

• RS Latch
• RS Flip Flop
• Bistable Flip Flop
 Not S Not R Q Not Q Comment 0 0 1 1 Unstable. Wil set or reset as soon as Not S or Not R goes high again. 0 1 1 0 If Not S is low, Q goes high and Not Q goes low. 1 0 0 1 If Not R is low, Not Q goes high and Q goes low. 1 1 0 or 1 1 or 0 Circuit remains in its previous stable state.

Here is the full circuit diagram and two alternative ways to draw the latch.

• If the "NOT S" switch is pressed, the top input goes low and the top NAND gate output goes high and stays high.
• If the "NOT R" switch is pressed, the bottom input goes low and the bottom NAND gate output goes high and stays high.
• If both switches are pressed, both outputs go high until one or other of the switches is released.
• This is good for debouncing because if R or S are pressed multiple times, only the first press has any effect.

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