Programmable Logic Devices

Design Procedure for Asynchronous Sequential Circuits :
• The design procedure used for the fundamental as well as the pulsed mode asynchronous sequential circuits is similar to the design process used for the synchronous sequential circuits.
• But note that, though the steps followed in the design procedure are similar, there are some differences as well.
• The main differences are the timing and input variable restrictions.

General design steps for asynchronous circuits :

The general steps to be followed for design of asynchronous sequential circuits are as follows :
1. Create a state table or state diagram from the given problem statement.
2. Create a new reduced state table by removing all the redundant states.
3. Create the transition table.
4. Write the excitation and output Boolean equations and simplify them.
5. Draw the logic diagram.

Flow Table :
• In the design of fundamental mode, the state table is modified into a flow table.
• The flow table represents the input, secondary and total states.
• Generally the initial state diagram is replaced with the flow table to determine total state transitions.

Additonal Information