OT: MC12080 prescaler chip weirdness

Michael Dunn

A Fluke counter I’ve been fixing up and adding homebuilt options to is missing the prescaler option. The vast majority of current chips seem to be binary, so, short of also dividing the reference clock, I decided to use a decade divider, an NOS MC12080 ÷10/20/40/80 chip.

Funny thing is, instead of dividing by 10, it’s dividing by 2! The chip internals consist of a fixed ÷5, followed by a programmable ÷2/4/8/16 stage. It’s like the ÷5 isn’t there, or is bypassed.

After some searching, I found a few other people bemoaning this exact same behaviour. So…at least I’m not crazy. Anyone here experienced something similar?

Gotta wonder what’s going on. Is there some sort of flaw in the chip design that leads to this failure mode? Was it a custom version? Hmm…


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