Changing the clock frequency slightly (PDP-11)?

Charles charlesmorris at
Sat Dec 31 14:41:28 CST 2005

>A common trick to change the frequence of a crystal, is to put a capacitor
>in parallel with it

You can "pull" a 27 MHz crystal (a few tens of KHz at most), but
that won't work with these integrated oscillators. They only have
three functional pins: +5, Gnd, Out...

Anyhow, while searching the junkbox for something completely
unrelated, I found a 30.000 MHz oscillator can. From the previous
discussion I figured it'd be worth a try... I tacked it in place
and voila - the RUN light lit briefly, and ODT promptly came up to
the "@" prompt!  :)

I can examine and change locations so at least the CPU and console
port are working. If anyone's got a short RAM test program I can
key in via ODT I'd appreciate it. The RAM is a Clearpoint card
that appears to be 2 Mbytes/1 Mword. (I don't know PDP-11 assembly
language, or machine code, so it's time to get out the manuals!)

Also the Fault light on the RL02 is still on, don't know if the
problem is in the drive or the RLV12 card yet. Guess I can swap
the other RL02 (working on the 8/A) and see what happens...


More information about the cctech mailing list