COUNTER
Counter are sequential circuits that keep record of the clock pulses sent. Counter consist of a group of flip-flops. It has characteristic internal sequence of state through which it passes if a series of clock pulses are applied to it. Ring counter is the most widely used shift register counter which is the basic ring counter as well as the twisted ring counter. MSI counters are of two type namely asynchronous counters and synchronous counters.
Ring Counters
Ring counter is the simplest shift register counter of the basic ring counter. The logic diagram for 4-bit ring counter using four D flip-flop is shown in the figure.
The Q output of each D FF is connected ti the D input of next D FF and the Q output of the last D FF is connected to D input of first D FF. IT is clear that the array of D FF is connected in a ring and therefore it is known as ring counter.
The figure of J-K flip-flop is shown in the figure
Similarly the Q output of each other J-K FF is connected to J input of next J-K FF and the Q output of last J-K FF is connected to the J input of first J-K FF. It is clear that the array of J-K FF is connected in a ring and therefore it is ring counter.
This is the only single 1 in the resister and it is circulated around the resister till clock pulses are applied. Initially the first FF is preset to 1.hence the initial state is 1000.
The state diagram of 4-bit ring counter is shown in the figure
The sequence table of 4-bit ring counter is show in the figure
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