As you study digital electronics, one of the first components you will encounter is the SR latch, a simple memory device that can hold a value of 1 bit. In digital electronics, latches are the fundamental memory device. SR latches, also known as Set-Reset latches, are some of the simplest ones that can be used to store one bit of data. Next we will explore how a gated SR latch and a clocked gated SR latch can make the SR latch a more useful device.
What is an SR Latch?
The SR Latch is a basic circuit that stores one bit of information.
It has two inputs:
- Set (S): Makes the output high (Q = 1)
- Reset (R): Makes the output low (Q = 0)
Once set, the output remains stable even if the inputs are removed — which is why it’s used as a memory element.
SR latches can be built using NOR gates or NAND gates:
Gated SR Latch
The Gated SR Latch is similar to the basic SR latch but includes an Enable input.
- When Enable = 1, the latch responds to S and R inputs.
- When Enable = 0, the output stays unchanged, regardless of inputs.
This provides more control and is often used in situations where the latch should only update at specific times.
Clocked SR Latch (SR Flip-Flop)
When a clock signal is introduced, the SR latch becomes edge-triggered, and is commonly called an SR Flip-Flop.
Here’s how it works:
- S = 1, R = 0 → Q = 1 (Set)
- S = 0, R = 1 → Q = 0 (Reset)
- S = R = 0 → Previous state (No change)
- S = R = 1 → Invalid condition
The clock ensures that the output only changes on a rising or falling edge, making it more reliable for sequential circuits.
Applications of SR Latch
- Basic memory storage elements
- Control circuits in microcontrollers and processors
- Debouncing switches in digital systems
- Building blocks for more advanced flip-flops (D, JK, T)
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