Changing the clock frequency slightly (PDP-11)?

[Don North]

I've used the Digiikey service to get a custom frequency (20.2752MHz,  
4x the 5.0688MHz clock frequency of a DL11-W). A little pricey (~$8  
each), but worked just as expected.

For your application though anything in the 25-27MHz should work just  
fine. If you are really adventurous put in a socket and get a few  
frequencies up to 33MHz or so and see how fast you can really go.

Clock chipping an oscillator based PDP-11 is a lot more  
straightforward than an older tapped delay line design like a 34, 44,  
etc.


On Dec 28, 2005, at 4:35 PM, J.C. Wren wrote:

>    You can order oscillators programmed with custom frequencies  
> from DigiKey, assuming you're speaking of oscillators and not a  
> crystal (I have someone at work who routinely interchanges the  
> terms, and it drives me up the wall).  They may not be in metal  
> cans, but they are available in the same foot print.  DigiKey can  
> have them to you as fast as you want to pay for shipping.
>
>    --jc
>
> Charles wrote:
>
>> After pulling out my hair for a while trying to get my PDP-11 to
>> talk to me, I finally discovered that the master clock (26.667 MHz
>> crystal oscillator) is dead. (KDF-11BA CPU board).
>>
>> Those metal-package oscillators are very common and inexpensive
>> (around $2), but I can't find one in that exact frequency. 25,
>> 25.175 and 27 MHz units are available. Semi-custom ones aren't
>> terribly much more expensive (~ $15) but have longer lead times.
>>
>> Is there anything in the circuitry that can't be run a little
>> slower (or 1.2% faster, 27 MHz)? I'm not worried about squeezing
>> every last MIPS out of it.
>>
>> thanks
>> Charles
>>
>>