11/23 clock issue

[Paul Anderson]

As i recall, dec would run cpu clocks till they failed, then back them off
20% or so. I had numerous customers who "modified" their cpus.

If you haven't found one yet, let me know. I should have a bow of them
here. And I know where they are!!!

Paul

On Sat, Feb 7, 2015 at 10:08 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:

> On 2015-Feb-07, at 11:20 AM, Holm Tiffe wrote:
> > Pete Turnbull wrote:
> >
> >> On 06/02/2015 07:44, Holm Tiffe wrote:
> >>> You don't ned no pullup for +5. All open TTL inputs are reading High
> w/o
> >>> any pullup.
> >>
> >> Yeah.  So someone at Commodore thought when they designed one version of
> >> the PET.  We had a few that erratically misbehaved.  It turned out that
> >> one input on a 74LS00 (I think it was) was floating, and switching noise
> >> made it erratic.  Floating inputs place the internal circuitry in an
> >> intermediate state, can cause increased current draw, typically slow the
> >> device down by increasing switching times, and can cause misbehaviour.
> >>
> >> TTL is supposed to have a 1K pullup (to limit possible transients);
> >> LSTTL can be directly connected to Vcc.
> >>
> >> --
> >> Pete
> >>
> >> Pete Turnbull
> >
> > Yes Pete, not all People over here are totally braindead.
> >
> > I've told him that he can leave out the +5V Connection for testing
> > purposes, for nothing other.
>
> No you didn't. While the context of the discussion is testing and that may
> have been your intention, your comment specified no such qualification, and
> as such at best left it ambiguous/unclear.
> Pete's comment was valid clarification and additional information
> (although I could have minor quibbles with some of the technical phrasing).
>
> Anyways (for Noel), everyone's right:
>
>         - An open TTL input will generally function or act as a logic high.
>           It was not unknown for designs to leave inputs open for
> static-state high,
>           but it is considered poor practice and can result in problems in
> some circumstances.
>
>         - Some sources specify using a pull-up R instead of direct
> connection to +5, but in practice many considered the R's as
> unnecessary/overkill.
>           Some designs used pull-up R's, some designs directly connect to
> +5.
>           I've even seen both in the same piece of equipment (probably
> multiple engineers involved in different parts of the design).
>
> This is for TTL (and DTL) only, MOS/CMOS is another matter.
>
>
> > That has nothing todo with your Commodore problem.
> >
> > Regards,
> >
> > Holm
>
>