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.
Counter in step 7 v5.6 mod#
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.
Counter in step 7 v5.6 free#
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