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Computer organization Notes

Difference between Combinational and Sequential Circuits

Combinational Circuits Sequential Circuits
1. In these circuits, output at any time depends only on the inputs applied at that instant of time. 1. In these circuits, output depends on the present input as well as past output.
2. It contains no memory elements. 2. It contains at least one memory element
3. It can be totally described by the set of output values only 3. It can be described by the output values as well as subsequent state values.
4. It is a combination of logic gates with a set of inputs and outputs. 4. It is a combination of flip flops & logic gates.
5. These are easy to design, due to simplicity of circuit. 5. These are complex to design due to presence of memory element.
6. These are faster in speed because of less delay time. 6. These are comparatively slow because of more delay time..
7. These need more hardware for its realization. 7. These need less hardware for its realization.
8. Due to more hardware, these are costly. 8. These are not so costly.
9. There is no feedback from output to input. 9. There is feedback from output to input
10. Operation can be described with truth table only 10.Operation can be described with truth table and timing diagram.
11. No clock signal is required for these circuits. 11. Clock signal is required for these circuits.
12. Examples are : Multiplexer, Adder, subtractor, decoder , encoder etc. 12. Examples are: Flip-Flops, Registers, counters etc.

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