26 Sep
2014
26 Sep
'14
2:27 p.m.
On Sep 26, 2014, at 3:57 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Given that, the answer is clear: get a crystal whose nominal frequency equals the one of
the original. You can probably ignore the trailing 5 since it?s not significant. (That
assumes it was an 0.01% tolerance crystal, as opposed to something more accurate so that 5
is significant. Chances are it?s 0.01, that?s plenty good enough for video timing.)
If you can?t find it off the shelf, just send in the quote request. I expect you?ll be
pleasantly surprised how cheaply you can get this electronic component, quantity one, made
to your specific spec.
paul
It depends on what is your definition of ?near enough?. If it?s a
clock crystal for a logic circuit that runs at about that speed, a 10 MHz
crystal might be fine. If the frequency controls some output frequency
In the TRS-80, the clock crystla _does_ determine the video timing. There
is one master clock (this one), divided down for the CPU clock and the
video RAM adressing and sync signals.
There si no real time clock in an unexpanded Model 1. Thre is a heartbeat
inerrupt produced by the Expansion Interface, but I think that has its
own crystal. In the M3 and M4, the heartbeat comes from the video
circuitry IRIC, so the one master crystal controls everything
-tony