How to Implement a Serial Adder using Mealy and Moore Machine in VHDL
A serial adder is a digital circuit that can perform binary addition on two numbers by processing one bit at a time. It is useful for applications that require low hardware complexity and high speed. In this article, we will show you how to implement a serial adder using Mealy and Moore machine in VHDL.
A Mealy machine is a type of finite state machine (FSM) that produces an output based on both the current state and the input. A Moore machine is another type of FSM that produces an output based only on the current state. Both Mealy and Moore machines can be used to design a serial adder, but they have some differences in terms of the number of states, the output delay, and the circuit complexity.
Serial Adder Block Diagram
The block diagram of a serial adder is shown below:
The serial adder consists of three shift registers that store the two input numbers A and B, and the output sum S. The shift registers are synchronized by a clock signal CLK. The adder FSM takes one bit from each input register at each clock cycle and produces one bit of sum and one bit of carry. The sum bit is shifted into the output register, while the carry bit is fed back to the next state of the FSM. The addition operation is completed when all the bits of A and B are processed.
Mealy Machine for Serial Adder
A Mealy machine for serial adder has two states: G and H, representing the carry-in values of 0 and 1, respectively. The output sum bit s depends on both the state and the input bits a and b. The state transition diagram of the Mealy machine is shown below:
The next state and output equations for the Mealy machine are:
Y = ab + ay + by
s = a â b â y
where Y is the next state variable, y is the current state variable, and â is the XOR operator.
The VHDL code for the Mealy machine is given below: