In the sequential circuit, the timing parameter comes into picture.
The output of a sequential circuit depends on the present time inputs, the previous output and the sequence in which the inputs are applied.
In order to provide the previous input or output a memory element is required to be used. Thus a sequential circuit needs a memory element.
Figure 1
Figure 1 shows the block diagram of a sequential circuit which includes the memory element in the feedback path.
Present state of sequential circuit: The data stored by the memory element at any given instant of time is called as the present state of the sequential circuit.
Next state: The combinational circuit operates on the external inputs and the present state to produce new outputs. Some of these new outputs are stored in the memory element and called as the next state of the sequential circuit.
The most important part of the sequential circuit seems to be the memory element. The memory element is known as flip flop (FF). It is the basic memory element.
Clock Signal: The clock signal is a timing signal. Every sequential signal will have this timing signal applied.
Clock is a rectangular signal with a duty cycle equal to 50%.
The clock signal repeats itself after every T seconds. Hence the clock frequency is f = 1/T.
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