overclocking older processors

From: Carlini, Antonio <Antonio.Carlini_at_riverstonenet.com>
Date: Tue Dec 11 16:12:40 2001

> Dave McGuire wrote:
>
> I was just reminded of when I overclocked an F11 chipset on a
>PDP-11/23 (KDF11-A) to 18MHz. It seems to me that it might be
>possible to overclock the 78032 on a KA630. Anybody ever done
that?

        I've just sent EK-78032-UG, basically the 78032 User Guide
        over to DFWCUG. You can see the gory details once
        it arrives and they put it up.

        In the meantime, from Appendix A, clock
        period is variable from 25ns to 250ns
        i.e. 40MHz to 4MHz. It specifically states
        (somewhere) that the part will *not*
        work down to DC.

        The clock should be held in the high
        and low states for 16ns each, so even with
        infinitely fast rise and fall you cannot do
        better than 32ns and stay reliable across
        all parts and all temperature ranges.

        Now if you are willing to restrict the
        temperature range and hope to work
        on just *most* parts, who knows :-)

        Tweaking a MicroVAX II won't buy
        you much. I doubt you could bump the
        clock by much more than say 20% without
        something going horribly wrong. And the
        uVAX II is a fairly well balanced system:
        the memory cycle is just about right for
        the CPU (I think it works out that the CPU
        cycle time matches the memory cycle
        time - hence no need for cache).

        So if you up the CPU clock, you need
        to find some way to speed up the memory
        otherwise you don't even see your
        modest 20% gain.

        Antonio
Received on Tue Dec 11 2001 - 16:12:40 GMT