Combinational and Sequential Logic Blocks

What:

These are the building blocks used in Digital Circuits to implement Logic Functions.

The Different Types:

Combinational Logic Blocks:

• Simply: Basic building blocks that don’t have any memory and whose output is a pure function of the present input only. Examples:
  • Logic Gates: AND, OR, NOT, NAND, NOR, XOR, XNOR.
  • Encoders-Decoders (Logic): Converting data from one format to another.
  • Comparators: Comparing values
• Quirks:
  • Instant output: The output changes immediately when the inputs changed.
  • Design: Typically designed with a Truth Table.

Sequential Logic Blocks:

• Formal: The present output depends on the present input as well as past input(s).
• Simply: These blocks have memory and their output is a function of the input as well as the history of past inputs, (the state). Lowkey just a Combinational Logic Block but with a memory bit added. Example:
  • Flip-Flops: These store a single piece of data. Like a light switch (more accurately light button), it will remember the previous state and only change when you give it a new ‘flip’ command.
    

But sir, the timing?

Because it’s half a combinational logic block, whenever you change the input, the state changes and thus the output could possibly change. This is known as asynchronous sequential logic.