Full Adder
Full adders are are digital circuits that adds binary numbers taking to account the numbers carried in and carried out. Full adders already have ready made ICs but here in this circuit we will construct the full adder using only logic gates. We will perform addition and subtraction of 4-bit binary numbers.
The schematic of a full adder is:
This schematic diagram is only applicable for adding 1-bit binary numbers. To add or subtract 4-bit binary numbers, the given circuit should be used four times by connecting the Cout to the Cin of the next full adder as seen in the diagram below:
where:
An - bits of the 1st 4-bit binary number
Bn - bits of the 2nd 4-bit binary number
Cin - carry in
Cout - carry out
The diagram above will result to an addition operation of a 4-bit binary number wherein the C0 is hanged or connected to the ground signifying a carry in of 0. To operate it as subtraction, we will use 2's complement. The 2nd binary number must be inverted and the last carry out will be the carry in of the 1st full adder.
The truth table for a 1-bit full adder will be:
The truth table for a 1-bit full adder will be:
Pictorials:
