Definition
SR Latch
An SR latch is composed of two cross-coupled NOR gates. The latch has two inputs,
and , and two outputs, and .
A NOR gate outputs false if one of the inputs is true. By walking through the possible cases, we can observe:
: produces and produces . : produces and produces . : and produce . : Since both inputs are , we can’t directly determine the outputs. However, we can try to understand the behaviour of the latch. Case 4a.) What if
? Case 4b.) What if
? We can use this two cases by introducing some known prior value, which we will call
, before we enter the third case. This prior value represents the state of the system. When , will remember this old value, and will be its complement . Thus, this circuit has memory.
Case 4 1 0 2 1 3 0 We call
set and reset signals. To simplify the circuit symbolism, we can represent the latch as:
