Examples of Designing of Synchronous Mod-N Counters

Here, we are going to have a look at how we can design synchronous mod-N counters using the procedure, we have studied in our previous article designing of synchronous counters.
Submitted by Saurabh Gupta, on March 26, 2021

Example 1: Design a mod – 5 synchronous counters using JK flip-flop.

Solution:

A mod-5 counter counts from 0 to 4. Thus, following the steps given in article - designing of synchronous counter, a mod-5 counter can be designed as:

Step 1: The number of flip-flops required to design a mod-5 counter can be calculated using the formula: 2n >= N, where n is equal to no. of flip-flop and N is the mod number. In this case, the possible value on n which satisfies the above equation is 3. Hence, the required number of flip-flops is 3.

Step 2: The type of flip-flop required to design the counter is JK flip-flop.

Step 3: We can draw the state diagram for mod-5 counter describing the state flow in current and next state as:

designing of synchronous mod n counters (1)

Step 4: Using the excitation table of JK flip-flop, we need to obtain the flip-flop inputs for each state that we obtained in the third step and now we will enter it into a table as:

designing of synchronous mod n counters (2)

Step 5: Making K-Map for each input combination and simplifying it to get the minimized Boolean expression.

designing of synchronous mod n counters (3)

Step 6: Using the Boolean expressions obtained in step 5, now we will draw the required counter circuit which can be shown as:

designing of synchronous mod n counters (4)

Example 2: Design a mod - 10 synchronous counter/ Decade counter/ BCD counter using T flip-flop

Solution:

A mod-10 counter counts from 0 to 9. Thus, following the steps given in the article - designing of synchronous counter, a mod-10 counter can be designed as:

Step 1: The number of flip-flops required to design a mod-10 counter can be calculated using the formula: 2n >= N, where n is equal to no. of flip-flop and N is the mod number. In this case, the possible value on n which satisfies the above equation is 4. Hence, the required number of flip-flops is 4.

Step 2: The type of flip-flop required to design the counter is T flip-flop.

Step 3: We can draw the state diagram for mod-10 counter describing the state flow in current and next state as:

designing of synchronous mod n counters (5)

Step 4: Using the excitation table of T flip-flop, we need to obtain the flip-flop inputs for each state that we obtained in the third step and now we will enter it into a table as:

designing of synchronous mod n counters (6)

Step 5: Making K-Map for each input combination and simplifying it to get the minimized Boolean expression.

designing of synchronous mod n counters (7)

Step 6: Using the Boolean expressions obtained in step 5, now we will draw the required counter circuit which can be shown as:

designing of synchronous mod n counters (8)

Example 3: Design a mod -12 synchronous up counter using T flip-flop

Solution:

A mod-12 up-counter counts from 0 to 11. As already seen in previous examples, we should follow similar steps and hence a mod-12 counter can be designed as:

Step 1: The number of flip-flops required to design a mod-12 counter can be calculated using the formula: 2n >= N, where n is equal to no. of flip-flop and N is the mod number. In this case, the possible value on n which satisfies the above equation is 4. Hence, the required number of flip-flops is 4.

Step 2: The type of flip-flop required to design the counter is T flip-flop.

Step 3: We can draw the state diagram for mod-12 counter describing the state flow in current and next state as:

designing of synchronous mod n counters (9)

Step 4: Using the excitation table of T flip-flop, we need to obtain the flip-flop inputs for each state that we obtained in third step and now we will enter it into a table as:

designing of synchronous mod n counters (10)

Step 5: Making K-Map for each input combination and simplifying it to get the minimized Boolean expression.

designing of synchronous mod n counters (11)

Step 6: Using the Boolean expressions obtained in step 5, now we will draw the required counter circuit which can be shown as:

designing of synchronous mod n counters (12)





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