ASIC Verification: Mod - 10 counter

Friday, April 18, 2008

Mod - 10 counter

A Mod-10 counter has 10 possible states, in other words it counts from 0 to 9 and rolls over. Let's take a look at how to build a Mod-10 counter.

The first step is to determine how many flip-flops to use. We will use JK FFs for our design. Since we need 10 states, 4 FFs will be required. The trick is to find a way not to use all of those states. There must be a way to force the counter to stop counting at 9 and roll over to 0. This is where an asynchronous inputs come into play. The asynchronous inputs can over-ride the synchronous inputs and force the outputs to either LOW or HIGH.

Looking at the truth table, the counter should run from 0000 to 1001 and roll over to 0000 again. Since the counter has to display 1001, the next binary value 1010 will be used to reset the counter to 0. For a JK FF, we have an asynchronous input called CLEAR, when you assert this, flop's output goes to 0. Since this CLEAR input is active high, we can use AND gate. The 2 FFs where a '1' occurs will be tied to an AND gate and the output will be tied to a CLEAR input. When the counter goes to 1001, the AND gate has a value '1' on its output and will activate the CLEAR inputs of all FFs.


simi said...

sir,try to give the will be very helpful for learning purpose

Anonymous said...

What about the clock signal? How does it divide the frequency of a input clock signal?

Anonymous said...

how can we make a mod 10 counter using mod 5 counter and mod 2 counter

Anonymous said...

how will you give me answer?

Anonymous said...


Anonymous said...

Much helpful... thanks.

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