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README.md
SRLatchWithNandGates.fzz

README.md

#346 DigitalLogic/SRLatchWithNandGates

Set-Reset latch implemented with NAND gates.

Here's a quick demo of it in action..

Build

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Notes

This circuit is another implementation of a Set-Reset flip-flip, this time using NAND gates. A 74LS00 is used to provide the two NAND gates required.

Other implementations:

The NAND gate implementatation has an undefined state with both inputs high, whereas a NOR gate implementatation has an undefined state with both inputs low.

Consequently NOR gates are typically used for active-high SR latches and NAND gates for active-low SR latches. A good example of this is the application in touch sensors, where active low makes sense. See the Boldport Club tap and mostap projects for examples of this.

Truth Table

Set(t) Reset(t) Output Q(t+1)
0 0 invalid state
0 1 1
1 0 0
1 1 Q(t) no change

sr-latch-nand

Construction

Here's a quick breadboard build using a 74LS00 quad two-input NAND gate, with some switches and LEDs to indicate S, R, Q and `Q:

Breadboard

Schematic

Build

Credits and References