I started designing 4-bit microprocessor in magic tool, it consists of three block:
- 4-bit full adder
- register to store an input data.
- 4-xor gates and one carrier input is used to 2’s complement for subtraction
Inputs which are used in it :
- two 4-bit data A and B
- carrier input
In this microprocessor, the adding operation is takes place when carrier input is 0, and the subtraction operation takes place when carrier input is 1. During subtraction, one’s complement block takes one’s complement B data and it send to 4_bit adder. The carrier input value is 1 at subtraction. so it’s form two’s complement of B data in 4-bit full adder.
And also sanjeev taugth me, to align block in order to reduce area and to create data bus with multiplexing two inputs.