SR Latch

SR Latch

A latch is the simplest sequential (memory) element. Unlike combinational circuits, its output depends on both current inputs and previous state.

The SR latch has two inputs:

• S (Set): forces output Q to 1
• R (Reset): forces output Q to 0

The SR latch holds its state when both inputs are 0. This is how single-bit memory works in digital circuits.

A function model takes the current state q and returns the next state:

function srLatch(s, r, q) {
  if (s === 1 && r === 0) return 1;  // set
  if (s === 0 && r === 1) return 0;  // reset
  if (s === 0 && r === 0) return q;  // hold
  return -1; // invalid
}

Your Task

Implement srLatch(s, r, q) that returns the next Q state (or -1 for invalid S=R=1).

Then simulate a sequence: start Q=0, apply Set, hold, hold, Reset, hold.