latch vs flip flop-Difference between latch and flip flop

This page compares latch vs flip flop and mentions difference between latch and flip flop. It mentions examples of SR latch with enable and SR flip flop in order to provide comparison between latch and flip flop.

SR Latch

SR latch with enable
Fig-1: SR Latch with Enable

The figure-1 depicts SR latch with enable using NAND Gates.
➨When E = 1, the circuit behaves like the normal NAND implementation of the SR latch except that the S and R inputs are active high rather than low.
➨When E = 0, the latch remains in its previous state regardless of the S and R inputs.

SR latch with enable timing diagram

In actual circuits, the enable input can either be active high or low, and may be named ENABLE, CLK, or CONTROL. A typical operation of the latch is shown in the timing diagram.
➨Between t0 and t1, E = 0 so changing the S and R inputs do not affect the output.
➨Between t1 and t2, E = 1 and hence changing the S/R will affect the output accordingly.

SR Flip flop

SR flip flop
Fig-2: SR Flipflop

We have seen in figure-1 that, output changes when enable signal is high and hence it is known as level triggered. When the Enable pin in figure-1 is replaced with clock input then the circuit acts as flip flop which is shown in the figure-2. The circuit in figure-2 is called flip flop only when clock goes from low to high or high to low. This is because circuit is operational during this edge transitions.

Master and Slave SR Flip flop

Master Slave SR flip flop
Fig-3: Master slave SR Flipflop

Both latches and flipflops are useful in setting and resetting the data bit. But unlike latches, flip flops will change the content at the active edge of clock signal only. When both the inputs are asserted simultaneously , like their latch (i.e. SR) counterpart, flip flop (i.e. SR) can enter into undefined state.

Tabular difference between latch and flip flop

Following table mentions similarities and difference between latch and flip flop.

Latch Flip flop
It is bistable device which stores either 0 or 1. It is also bistable device which stores either 0 or 1.
Flip flop changes state only during the clock signal. Latch changes state as soon as input is given and does not depend on control input or clock input i.e. there is no clock present in latch.
In flip flop, there is control over operation using clock signal. In latch, there is no control over operation unless we desire to have with the help of enable signal.
Based on edge triggering (low to high transition or high to low transition) there are two types of flipflops viz. positive edge triggered and negative edge triggered. There is also type of flip flop which triggers based on pulse middle part known as pulse triggered flip flop. The latch which gets activated based on enable signal (in logic high state) and remains in deactivated state when enable signal is low; is known as gated latch.
Examples of flip flops are D flip flop, T flip flop, SR flip flop, JK flip flop Examples of latches are D latch, T latch, SR latch, JK latch

Flip flop VHDL Verilog source codes

D Flipflop with synchronous reset verilog code
D Flipflop without reset verilog code
Flip flop conversion equations
D Flipflop
T Flipflop
JK Flipflop

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