How does the sr latch work?

The SR latch (also known as the basic RS flip-flop) is the simplest structural form among various flip-flop circuits. At the same time, TA is also one of many complex circuits. The basic building blocks of structural triggers.(Recommended study:phpstorm)

The RS latch is a circuit with one or two inputs and two outputs. The circuit is as shown in Figure a below, with two crosses. It is composed of two NAND gates connected by feedback, and its two outputs are two opposite outputs (or called complementary outputs). Figure b shows its logic symbol.

In the figure, /RD and /SD are the two input terminals of the RS latch, Q and /Q are two complementary outputs, from the figure It is not difficult to see that the output state does not change when /RD and /SD are high level, but the output changes only when one of its inputs is low level, so /RD and /SD are active low level.

Let’s take a look at the working process of the RS latch. We can discuss it in four situations:

1. /RD=0, /SD=0

It can be seen from the circuit that when /RD=0,/SD=0, Q=/Q=1, and the latched Q and /Q are two Complementary output, and now the two outputs are equal, this is not allowed, so this situation is not allowed for the latch, so it is usually called an impermissible state;

2./RD=0,/SD=1

Since /SD=1, the state of Q depends on the state of /Q, and since /RD=0,/Q=1, Therefore Q=0, so when /RD=0,/SD=1, the flip-flop is set to 0, so it is called the set-0 state;

3./RD=1,/SD= 0

This is exactly the opposite of the previous situation. Its Q=1,/Q=0, that is, the flip-flop is set to 1, so it is called the set state;

4./RD=1,/SD=1

Since the input of RS is active low level, and now both inputs are high level, its output state remains unchanged. , called the holding state.

The above RS latch is composed of NAND. A NOR gate can also be used to form an RS latch, and the function of the RS latch can also be realized.

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