Types of Latch in Digital Electronics

Latch in Digital Electronics:

The simplest kind of a sequential circuit has only two states. It is a memory cell that is capable of storing one bit of information. This sequential circuit is also called a latch since one bit of information can be locked or latched. The basic latch consists of two inverters as shown below figure:

Types of Latch:

i. S-R Latch: The S-R latch has two inputs named SET (S) and RESET (R) and two outputs Q and Q’. The outputs are a complement to each other.

ii. NOR-based S-R Latch: The S_R latch can be easily constructed using two NOR gates connected back to back. The cross-coupled connections from the output of one gate to the input of the other gate constitute a feedback path. For this reason, the circuits are classified as Asynchronous Sequential Circuits. The truth table for the NOR-based S_R latch is shown below:

iii. NAND-based S-R Latch: It is constructed by using cross-coupled NAND gates. The operation of the NAND S-R latch can be analyzed in the same manner employed for the NOR latch. To understand the operation of the NAND-based S-R latch, one must remember that a low at any input of the NAND gate will force its output to high. The truth table for the NAND-based S-R latch is shown below: