A Counter is probably one of the most useful and versatile subsystems is a digital system.A Counter can be describe as a tallying devices that tallies or counts some number of events.A counter driven by a clock can be employed for counting the number of clock cycles.Since the clock pulses occur at fixed and known intervals,the counter can be used as a digital instrument to measure time and therefore period of frequency.Besides,wide applications in digital instrumentation,counters are also used to generate timing sequence for controlling the sequential logic operations.
A binary counter is made with a group of flip-flops arranged in a predetermined manner.Count pulses are supplied to clock input terminal of flip-flop either by a clock of fixed frequency or at random by some other source.These count pulses are counted by the counter in binary form.Since a flip-flop has two possible states,an array of n flip-flops has 2^n states and counts from 0 to 2^n-1 numbers in binary form.
Basically the counters are of two types,namely,asynchronous(or serial) and synchronous (or parallel) counters.
An example of an asynchronous counter is the ripple counter .When the output of one flip-flop drives another flip-flop drives another flip-flop,the counter is called a ripple counter.The ripple counter is simple and straight forward in construction and operation and usually needs a minimum of hardware.The drawback of such a counter is speed limitation.Each flip-flop is triggered by the previous flip,and thus the counter has a cumulative setting time.
An increase in operating speed can be had by using a parallel or synchronous counter in which every flip-flop is triggered by the clock in synchronism.The increase in speed is usually obtained at the cost of increased hardware.
Serial and parallel counters are used in combination to compromise between speed of operation and hardware used.Serial,parallel or combination counters can be designed such that each clock pulse advances the contents of the counter by one;it is then said to e operating in count-up mode.The opposite is also possible;the counter is then said to e operating in count-down mode.
A binary counter is made with a group of flip-flops arranged in a predetermined manner.Count pulses are supplied to clock input terminal of flip-flop either by a clock of fixed frequency or at random by some other source.These count pulses are counted by the counter in binary form.Since a flip-flop has two possible states,an array of n flip-flops has 2^n states and counts from 0 to 2^n-1 numbers in binary form.
Basically the counters are of two types,namely,asynchronous(or serial) and synchronous (or parallel) counters.
An example of an asynchronous counter is the ripple counter .When the output of one flip-flop drives another flip-flop drives another flip-flop,the counter is called a ripple counter.The ripple counter is simple and straight forward in construction and operation and usually needs a minimum of hardware.The drawback of such a counter is speed limitation.Each flip-flop is triggered by the previous flip,and thus the counter has a cumulative setting time.
An increase in operating speed can be had by using a parallel or synchronous counter in which every flip-flop is triggered by the clock in synchronism.The increase in speed is usually obtained at the cost of increased hardware.
Serial and parallel counters are used in combination to compromise between speed of operation and hardware used.Serial,parallel or combination counters can be designed such that each clock pulse advances the contents of the counter by one;it is then said to e operating in count-up mode.The opposite is also possible;the counter is then said to e operating in count-down mode.
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