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The main difference between a combinational circuit and a sequential circuit is that in the sequential circuit there is a feedback from one or more of the outputs to one or more of the inputs. See the following picture.
You can see that the output of the OR gate is feedbacked to the input of the lower AND gate.
This means that the F output depends on the inputs A and B and on the value it has previously.(Fo)
The truth table would generally be like the one below, where the inputs are: A, B and the previous output F. (Fo)
The output F is the current output. (look at the following truth table)
Note: It is important to know that although the previous output column Fo shows "0" and "1" for all combinations of A and B, this is not necessarily true.
Related Links
- Logic Circuit
- Logic Levels
- Analog and Digital. What´s the difference?
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