![]() The output of the first flip flop will change, when the positive edge of clock signal occurs. Here Q0, Q1, Q2, Q3 represents the count of the 4 bit down counter. The other flip flops in counter receive the clock signal input from Q output of previous flip flop, rather than Q’ output. The clock input is connected to first flip flop. That means the flip flops will toggle at each active edge (positive edge) of the clock signal. ![]() The clock inputs of all flip flops are cascaded and the D input (DATA input) of each flip flop is connected to logic 1. 4 bit DOWN counter will count numbers from 15 to 0, downwards. It is simple modification of the UP counter. Timing diagram of Asynchronous counterįor example, if the present count = 3, then the up counter will calculate the next count as 4.Ī 4 bit asynchronous DOWN counter is shown in above diagram. As this circuit is 4 bit up counter, the output is sequence of binary values from 0, 1, 2, 3….15 i.e. Now if we apply the fourth clock pulse, it will make the Q0 and Q1 to low state and toggles the FF2. So now both Q0 and Q1 are high, this results in making the 4 bit output 11002. In this way the next clock pulse will make the Q0 to become high again. This makes the output of FF1 to be high (i.e. This means the output state of the clock pulse toggles (changes from 0 to1) for one cycle.Īs the Q’ of FF0 is connected to the clock input of FF1, then the clock input of second flip flop will become 1. When the rising edge of the clock pulse is applied to the FF0, then the output Q0 will change to logic 1 and the next clock pulse will change the Q0 output to logic 0. Let us assume that the 4 Q outputs of the flip flops are initially 0000. ![]() Working of asynchronous up counter is explained below, The Q outputs of every individual flip flop (Q0, Q1, Q2, Q3) represents the count of the 4 bit UP counter such as 20 (1) to 23 (8). It triggers the next clock frequency to half of its applied input. The rising edge of the Q output of each flip flop triggers the clock input of its next flip flop. In the asynchronous 4- bit up counter, the flip flops are connected in toggle mode, so when the when the clock input is connected to first flip flop FF0, then its output after one clock pulse will become 20. The output of the first flip flop will change, when the positive edge on clock signal occurs. The other flip flops in counter receive the clock signal input from Q’ output of previous flip flop. That means the flip flops will toggle at each active edge or positive edge of the clock signal. The clock inputs of all flip flops are cascaded and the D input (DATA input) of each flip flop is connected to a state output of the flip flop. It is capable of counting numbers from 0 to 15. They areĪ 4 bit asynchronous UP counter with D flip flop is shown in above diagram. There are many types of Asynchronous counters available in digital electronics. So it is called as “MOD-4 counter” or “Modulus 4 counter”. The maximum number of states that a counter can have is 2n where n represents the number of flip flops used in counter.įor example, if we have 2 flip flops, the maximum number of outputs of the counter is 4 i.e. The number of output states of counter is called “Modulus” or “MOD” of the counter. The number of flip flops used in a ripple counter is depends up on the number of states of counter (ex: Mod 4, Mod 2 etc). Another name for Asynchronous counters is “Ripple counters”. The required number of logic gates to design asynchronous counters is very less. Because the flip flops in asynchronous counters are supplied with different clock signals, there may be delay in producing output. Different types of Asynchronous countersĪsynchronous counters are those whose output is free from the clock signal.In timing diagram Q 0 is changing as soon as the negative edge of clock pulse is encountered, Q1 is changing when negative edge of Q 0 is encountered(because Q 0 is like clock pulse for second flip flop) and so on. Every time Q 1 goes from 1 to 0, it complements Q 2, and so on. Every time Q 0 goes from 1 to 0, it complements Q 1. The lowest-order bit Q 0 must beĬomplemented with each count pulse. Or when the output to which it is connected goesįrom 1 to 0. In the CP input indicates that the flip-flopĬomplements during a negative-going transition All J and K inputs are equal to 1.įig: 4-bit ripple counter using JK Flip Flop The diagram of a 4-bit binary rippleĬounter is shown in Fig. Holding the least significant bit receives the incoming count pulses. The output of each flip-flop connected to the Clock Pulse input of the next higher-order flip-flop. Explain the 4 bit ripple counter and also draw a timing diagram.ġ0 Mark question | Asked in (TU CSIT) Digital LogicĪ binary ripple counter consists of a series connection of complementing flip-flops (T or JK type), with
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