Hence a 3-bit counter is a mod-8 counter.Ī mod-n counter may also be described as a divide-by-n counter.
7474 RISING EDGE TRIGGERED FLIP FLOP MOD
The number of states that a counter owns is known as its mod (modulo) number. Similarly, a counter having n flip-flops can have a maximum of 2 to the power n states. The 3-bit ripple counter used in the circuit above has eight different states, each one of which represents a count value. The following counter will toggle when the previous one changes from 1 to 0 In the circuit shown in above figure, Q0(LSB) will toggle for every clock pulse because JK flip-flop works in toggle mode when both J and K are applied 1, 1 or high input. When counting down the count sequence goes in the opposite manner: 111, 110, … 010, 001, 000, 111, 110, … etc.Ī 3-bit Ripple counter using JK flip-flop – When counting up, for n-bit counter the count sequence goes from 000, 001, 010, … 110, 111, 000, 001, … etc. The sequence of counting usually gets repeated after a limit.
The flip-flop applied with external clock pulse act as LSB (Least Significant Bit) in the counting sequence.Ī counter may be an up counter that counts upwards or can be a down counter that counts downwards or can do both i.e.count up as well as count downwards depending on the input control. Only one flip-flop is applied with an external clock pulse and another flip-flop clock is obtained from the output of the previous flip-flop. All the flip-flops are used in toggle mode. Different flip-flops are used with a different clock pulse. Some of the features of ripple counter are: It is known as ripple counter because of the way the clock pulse ripples its way through the flip-flops. So they are elementary in design and also are less expensive.Ī n-bit ripple counter can count up to 2 n states. In this, the flip-flops are asynchronous counters and are supplied with different clock signals, there may be a delay in producing output.Īlso, a few numbers of logic gates are needed to design asynchronous counters. It can also be used for Frequency divider, time measurement, frequency measurement, distance measurement and also for generating square waveforms. Prerequisite – Counters, n-bit Johnson CounterĪ counter is basically used to count the number of clock pulses applied to a flip-flop. ISRO CS Syllabus for Scientist/Engineer Exam. ISRO CS Original Papers and Official Keys. GATE CS Original Papers and Official Keys.
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