Combinational and Sequential circuits are the most essential concepts to be understood in digital electronics.
Combinational logic (sometimes also referred to as time-independent logic) is a type of digital logic which is implemented by Boolean circuits, where the output is a pure function of the present input only.
Sequential logic is a type of logic circuit whose output depends not only on the present value of its input signals but on the sequence of past inputs.
|Combinational Logic Circuits||Sequential Logic Circuits|
|Output is a function of the present inputs (Time Independent Logic).||Output is a function of clock, present inputs and the previous states of the system.|
|Do not have the ability to store data (state).||Have memory to store the present states that is sent as control input (enable) for the next operation.|
|It does not require any feedback. It simply outputs the input according to the logic designed.||It involves feedback from output to input that is stored in the memory for the next operation.|
|Used mainly for Arithmetic and Boolean operations.||Used for storing data (and hence used in RAM).|
|Logic gates are the elementary building blocks.||Flip flops (binary storage device) are the elementary building unit.|
|Independent of clock and hence does not require triggering to operate.||Clocked (Triggered for operation with electronic pulses).|
|Example: Adder [1+0=1; Dependency only on present inputs i.e., 1 and 0].||Example: Counter [Previous O/P +1=Current O/P; Dependency on present input as well as previous state].|