allison wrote:
On 05/30/2013 03:09 AM, Holm Tiffe wrote:
Roe Peterson wrote:
Does anyone have information regarding modifying a
pdp11/93 cpu to run
at 20Mhz? It's been mentioned on a couple of web pages, but I can't
seem to find details.
Thanks!
--
There isn't much of detail to tell, simply replace the 18Mhz Xtal
against a 20Mhz one, but be warned, the CPU isn't the only limiting
factor for the speed, the Gate Arrays and the FPU are also involved.
Maybe you toast them while overclocking..
I've changed th 15Mhz Xtal from an 11/73 CPU to 18Mhz to get a 11/83..
Regards,
Holm
The biggest thing with that kind of speedup is first its a trivial
amount and
the other is if you go too far system reliability will be poor and show
up as
unexpected crashes with known solid software (data errors).
That said I've pushed the clock on 11/23 board once too see and the 13mhz
clock was wound up to 25mhz using a external source. I started seeing
errors above 18mhz but they were random, seems bus timing and memory
timing all had to be happy and I was pushing the margins. I eventually
put in a clock module for 15.8mhz as I had one. For that it was a modest
speed up as the 11/23 is slower to start with.
Generally overclocking is problematic because the system timing is based
on it
and there may be items other than the CPU that have lower limits.
Allison
Yes. In my case I've changed the older J11 to one of the last available
revisions (-09?) to be at least sure that it meets the specifications.
I don't had another FPU Chip so the FPU and the Gate Arrays are the 15Mhz
Versions. Tested the entire Machine with all available Test Programms on
xxdp to be sore the entire system works as expected...no error so far..
Regards,
Holm
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