# Synchronous Counters ET 5. Thinking back In the past we have seen that asynchronous counters can be used to count binary in the order that we have filled.

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Synchronous Counters ET 5

Thinking back In the past we have seen that asynchronous counters can be used to count binary in the order that we have filled in truth tables and the same we count in our day to day lives. The binary can then be converted into decimal notation using a Binary to Decimal Decoder.

Disadvantages There is a problem with using these types of counters. If we need a high degree of accuracy in terms of the times when the outputs light up then asynchronous counters are not an ideal solution. The clock input of one flip flop is dependant on the output from another flip flop. Due to the propagation delay of each flip flop, this can cascade further down our circuit until our counting system is no longer accurate (in terms of time) Synchronous counters use the clock in a different way Asynchronous counter

Example You have been asked to design a system that creates the following light pattern. You must be able to create the following from the information given A state diagram A truth table The boolean expression A circuit diagram You may be given any of these items and be asked to create the rest from that information. Note One possible state has not been used……… 0 0 01 10 11

The State Diagram First you must decide how many different states can be created from the number of bits available. You must then work out which states are UNUSED in the sequence you have been given. The system could settle in any state and so if it starts off in an unused state it must be DRIVEN to a used state. The system must never come back to an unused state again. 01 10 11 00 Unused state

The Truth Table First you must decide how many different states can be created from the number of bits available. You must then work out which states are UNUSED in the sequence you have been given. The system could settle in any state and so if it starts off in an unused state it must be DRIVEN to a used state. The system must never come back to an unused state again. 01 10 11 00 Unused state

Question 1

Question 1 Truth Table

Gray Code

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