17-04-2014, 03:29 PM
To study and design of MOD-100 counter using IC 7490.
Theory :
The digital circuit used to count the number of clock pulses is known as a counter. The counters are designed using flip-flops. The modulus of a counter is the number of states the counter has. A counter with n flip-flops has maximum up to 2n states. Counters are basically divided into two types.
1) Asynchronous counter
2) Synchronous counter
In asynchronous counter all the flip-flops are not clocked simultaneously. The clock signal is applied to one flip-flop and the output of the preceding flip-flop is connected to the clock input of the next flip-flop.
In synchronous counters all the flip-flops are clocked simultaneously.
Depending on the way in which the counting progresses, the synchronous or asynchronous counters are classified as follows:
Up counter
Down counter
Up/Down counter
IC 7490 : IC 7490 is a TTL MSI decade counter. It is a 14 pin IC. It contains four master slave flip-flops and additional gating to provide a divide-by-two counter and a three stage binary counter which provides a divide-by-five counter. Each decade counter is a MOD-10 counter. If we want to increase the MOD number beyond 10 , we have to cascade more than one IC 7490.
Design of MOD-100 counter :
MOD-100 counter can be obtained by cascading two decade counter ICs as shown in fig.
Each IC gives 10 counts. Hence two ICs will give 10 x 10 = 100 counts. Both the ICs are in their normal divide-by-10 mode i.e. clock is applied to the input A of IC 7490 –(1), the QA output is connected to B input. For cascading, the QD output of the first IC is connected to the input A of the second IC. Thus QD of IC - (1) acts as clock input to IC – (2). For IC – (2) also the QA output is being connected to B input. The R0(1), R0(2),R9(1) and R9(2) inputs of both ICs are connected to ground so as to make them inactive. The total count provided by the two counters varies from 00 to 99 decimal that means 100 states. Hence it is a MOD-100 counter. The frequency of QD output of IC – 2 will be equal to fclk/100. Hence it is also called as divide-by-100 counter.
Conclusion:
Thus we have designed and studied the working of MOD-100 counter using two MOD-10 counters.