15 Dec
2014
15 Dec
'14
6:32 a.m.
Simon C. wrote:
I've taken the electronics module apart as I want
to find out where the clock
is generated or derived from as there is no xtal on the machine and there is
no ac from the psu going to the electronics.
The clock is likely derived from a simple R/C oscillator, with some buffer drivers
on the output(s) to provide enough drive current to feed the clocked logic of the machine.
No crystal is really needed.
Variations in clock speed over time isn't really a big deal with electronic
calculators. The key thing is that the designs based on delay lines usually have some
kind of timing bit(s) that are injected into the delay line that help sync the timing of
the delay line with the rest of the clocked logic.
Most old electronic calculators had main clock speeds (which was generally always divided
down to various phases) in the 40KhZ to 100KHz range. Even at these modest speeds, it
was easy for the machines to be much faster than the mechanical machines that they very
quickly made obsolete.
-Rick Bensene