вид 5 разрядного регистра jk

A 4-bit synchronous counter using JK flip-flops

The use of flip-flop outputs as clocks leads to timing skew between the count data bits, making this ripple technique incompatible with normal design styles.

You can continue to add additional flip-flops, always inverting the output to its own input, and using the output from the previous flip-flop as the clock signal. The result is called a ripple counter, which can count to 2n пІБ‚¬БЂ™ 1 where n is the number of bits (flip-flop stages) in the counter. Ripple counters suffer from unstable outputs as the overflows "Ripple" from stage to stage, but they do find frequent application as dividers for clock signals, where the instantaneous count is unimportant, but the division overall is (to clarify this, a 1-bit counter is exactly equivalent to a divide by two circuit; the output frequency is exactly half that of the input when fed with a regular train of clock pulses).

An asynchronous (ripple) counter is a single , with its J (data) input fed from its own inverted output. This circuit can store one bit, and hence can count from zero to one before it overflows (starts over from 0). This counter will increment once for every clock cycle and takes two clock cycles to overflow, so every cycle it will alternate between a transition from 0 to 1 and a transition from 1 to 0. Notice that this creates a new clock with a 50% at exactly half the frequency of the input clock. If this output is then used as the clock signal for a similarly arranged D flip-flop (remembering to invert the output to the input), one will get another 1 bit counter that counts half as fast. Putting them together yields a two-bit counter:

Asynchronous counter created from two

[ ] Asynchronous (ripple) counter

Counters are useful for digital clocks and timers, and in oven timers, VCR clocks, etc.

Occasionally there are advantages to using a counting sequence other than the natural binary sequenceпІп‚БЂ«such as the counter, a counter, or a counter.

Each is useful for different applications. Usually, counter circuits are in nature, and count in . Many types of counter circuits are available as digital building blocks, for example a number of chips in the implement different counters.

Johnson counter пІп‚БЂњ a twisted ring counter

Ring counter пІп‚БЂњ formed by a shift register with feedback connection in a ring

Up/down counter пІп‚БЂњ counts both up and down, under command of a control input

Decade counter пІп‚БЂњ counts through ten states per stage

Synchronous counter пІп‚БЂњ all state bits change under control of a single clock

Asynchronous (ripple) counter пІп‚БЂњ changing state bits are used as clocks to subsequent state flip-flops

In , counters can be implemented quite easily using register-type circuits such as the , and a wide variety of classifications exist:

In and , a counter is a device which stores (and sometimes displays) the number of times a particular or has occurred, often in relationship to a .

This article is about the term counter used in electronics and computing. For other uses, see .

From Wikipedia, the free encyclopedia

Counter - Wikipedia, the free encyclopedia