I think TS has long ago forgotten that he ever asked the question.

 

Zero research was invested before the question was asked,
so it's just as well.
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Better yet, use a small CPLD or FPGA, you can implement all the logic and even change it if you want to count up in Hex or just about anything else you can imagine.

That has nothing to do with the OP's question. S/he just wanted to know how a circuit worked. Personally, I think we should answer the OP's question, not suggest other ways to do something.

The days of using dedicated discrete digital logic IC chips are long past gone.

On what do you base this statement? I still use discrete digital IC's, sometimes in concert with Arduino's, RPi's, and other microcontrollers.

 

'"" Personally, I think we should answer the OP's question, ""

I think the Thread-Starter left the building about 3-days ago,
and left behind a bunch of nerdy Electronics guys standing around
drinking Coffee and shooting the breeze.
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That has nothing to do with the OP's question. S/he just wanted to know how a circuit worked. Personally, I think we should answer the OP's question, not suggest other ways to do something.

On what do you base this statement? I still use discrete digital IC's, sometimes in concert with Arduino's, RPi's, and other microcontrollers.

When I worked for Raytheon Missile Systems during my 20 years there. All of our designs used either CPLD's or FPGA's depending what type of digital complexity was involved. We also used Microcontrollers and ARM processors. Rarely did we use discrete digital chips. You have a point. Some markets are still possibly using discrete digital IC's. I just think they are far inferior to a chip that I can create any digital logic circuit I feel like with little effort. As to the OP's question, I agree with zophas, it appears they have long forgotten about the problem. Not to mention multiple people have already answered how it works in this forum multiple times.