This sequential circuit contains a set of inputs and output(s). The output(s) of sequential circuit depends not only on the combination of present inputs but also on the previous output(s). Previous output is nothing but the present state. Therefore, sequential circuits contain combinational circuits along with memory (storage) elements. Some sequential circuits may not contain combinational circuits, but only memory elements.
Following table shows the differences between combinational circuits and sequential circuits.
|Combinational Circuits||Sequential Circuits|
|Outputs depend only on present inputs.||Outputs depend on both present inputs and present state.|
|Feedback path is not present.||Feedback path is present.|
|Memory elements are not required.||Memory elements are required.|
|Clock signal is not required.||Clock signal is required.|
|Easy to design.||Difficult to design.|
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