Operation of the MM74C90 (4-bit decade counter)

[nwo4life]

Hi,

I was wondering how the MM74C90 4 bit decade counter works and how to use it. I have raed the data sheets but I stil don't know how to use it lets say for a divide by 5 frequency counter. I have searched google and got no help from it.

THANKS for any Help

 

[ted]

Hi nwo4life,

It seems, that you have pretty little experience with digital ICs? Well, everyone has to start from the beginning. As I assume, that this the very beginning for you, I'll give some generic hints and advice on quite a basic level:

MM74C90 is a CMOS asynchronous decade counter. This particular family is quite old, and has a wide operating voltage range: 3 to 15 V. Mostly it is used with 5 V supply on the Vcc pin.
The input signals MUST be between the supply rails (ground and Vcc).

The counter has internally two parts: A divide-by-2 and a divide-by-5 part, which, when used together, form a divide-by-10 counter.

The divide-by-5 part has a slightly elaborate reset (to 0) and preset (to 9) circuit. I will not explain in details the function, but it is pretty easy to analyze, if you can the logic circuits and Boolean functions.

For normal operation, the Reset and Preset inputs R01,R02, R91, R92 should be held to ground. Then you may feed the input frequency to pin Bin, and the pin Qd will provide an output frequency of one fifth of that.

If you ant to build a practical circuit, remember the input levels, and also remember to have a so-called bypass capacitor between VCC and ground close to the IC. A ceramic capacitor of 100 nF should work well with this kind of slowish logic.

Good luck!

--ted