The output is actually a voltage between 0V and 5V. This is supplied to the ECU of a motorbike. The current circuit I am using uses an NE555 to clock the pot and it doesn't seem to care if the clock pulses are there continuously. It has been working for about 5 years with no problem. Just me being a tinkerer I wanted to try and make it even smaller. If I can do it with an ATTiny 25/45/85 and the pot with a few other discrete components then I will be happy. So I can't see why I would need to count pulses, hence why I just wanted some form of clock pulse (now 128Hz) to clock the pot. CS can be set to be on permanently as it is now and control the U/D with the 85. I was trying to make it as small as I could with the smallest code.
I appreciate all the suggestions and it helps me learn although they did say you can't teach old dogs new tricks.