**Combinational circuits** can be defined as a circuit whose output is dependent only on the combination of the inputs at the same instant of time.

In **combinational circuits** past values of inputs or outputs is not required in the present output that is why **combinational circuits** have no memory, timing or feedback loops. In combinational circuits any changes to the signals being applied to their inputs have direct effects at the output.

**Applications of combinational circuits are** –

- Perform Arithmetic, logic, shift operations.
- Perform data transfer functions (like multiplexing, demultiplexing etc.)
- Perform Conversions (like gray to binary, Excess-3 to gray etc.)

## Half Adder

A half adder is a logical circuits that performs an additions operation on two binary digits. It produces two outputs, S(sum) and c(carry). So you can say that half adder is a combinational circuits that takes two inputs and produces two outputs.

## Full Adder

A full adder is a **combinational circuits** that performs an addations an addition on three binary digits. Full adder consists three data inputs and two outputs (sum and carry).

## 4-bit binary incrementer

A 4-bit increamenter adds a single bit 1 to 4-bits number say A3, A2, A1, A0 Increment microoperation is implemented with the help of combinational circuits half adder. The diagram of 4-bit combinational circuit incrementer is shown in fig.3.1.