27 Jul
2012
27 Jul
'12
10:59 p.m.
Nick Allen wrote:
Is there any reason to use either a CMOS or TTL
Crystal Oscillator for
a Cosmac computer? I assume it should accept either, any preference
if you had a choice?
There's no reason to use either. Just use a crystal. I don't remember
ever seeing an 1802 system with a separate oscillator, though it's
certainly possible to do it.
If you feel that you *must* use a separate oscillator, and you're
running the 1802 at 5.0V, then you should use a 5V CMOS oscillator,
because the Vih spec is 3.5V min, and TTL outputs don't typically go
that high. You might be able to get away with a TTL oscillator with a
pullup resistor.