Re: CIA old/new?

From: groepaz_at_gmx.net
Date: Thu, 07 Jan 2021 19:11:36 +0100
Message-ID: <1961538.IDvDuAF1LB_at_rakete>
Am Donnerstag, 7. Januar 2021, 18:54:12 CET schrieb silverdr_at_wfmh.org.pl:
> > On 2021-01-07, at 04:12, Segher Boessenkool <segher_at_kernel.crashing.org>
wrote:
> >>> I assume this is the line that goes from CS to the "VIC" pin on the new
> >>> PLA on a 250469? Trace cut and put cap between them?
> >>
> >> No. You'd have to put a cap between the /CS on the VIC and GND.
> >
> > Yup.  Just a low-pass filter, used as a crappy delay.  I would put it
> > close to the pin on the VIC, but that may not matter much.
> >
> >> You shouldn't do that though.
> >
> > We only did it to show what causes the problem, yup.
>
> As I mentioned already in this thread - only (some) of the HMOS-II chips
> expose the problem. Among those which do, it may depend on the chip's
> temperature (problem fades with temperature rising). OTOH no single NMOS
> based VIC expose the issue even with the same board timing. Yes, you can
> patch the _CS line with a cap and crudely work the problem around this way
> but I say it once again: with the very same _CS timing no NMOS VIC produces
> the annoying sparkles. So it is up to whoever reads this to decide whether
> this is a bug of the board/PLA/replacement or the actual HMOS-II VIC. For
> me it's the latter.

yep. can easily be checked on a board that supports both.

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Received on 2021-01-07 20:00:02

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