Re: Two projects

From: Frank Kontros (
Date: 1998-03-20 02:43:54

Ruud Baltissen wrote:

>The first problem I encounterd was that the card I built could be seen by
>my XT, 286 and my Pentium but not by my 386.

That's also common problem for most EPROM programmers on PC, because of
different CPU to I/O delays. I also encountered same problem with some
VGA cards (!). Some cards works without problem with 286, 486 and Pentium's,
but nor with 386's :-)

>The third problem was that after replacing the lines I still didn't
>recognise the data on the bus. After some puzzling I found out that all
>bytes were inverted. This puzzled me because this simply meant that the
>byte was inverted on purpose because writing a byte directly to the PIA
>appears as so on the bus. This also means that an attached device has to
>invert it again to get the original byte. Has anybody an idea why this is

That is because of inverted logic of IEEE-488 bus standard. I'm sure in that,
why recall my diploma project. (If you told me earlier... :) Most of C64 IEEE
interfaces uses inverting by 'software'. Maybe this because of few bi-dir
bus drivers in 74xx TTL series.

>At the moment I'm expanding my PRG at the PC so it will show the behaviour
>of all lines during a transfer. Here I encounterd an other problem. Even
>using my Pentium neither Pascal nor C are fast enough to scan all lines
>quick enough to see all changes. So I have to program in assembler.

There are specialized IEEE-analizers, but who have at least one? The ROM
listings also good sources, if they drives simple port logic and not an
specialized GPIB controller chips.

>The second project, X-DMA, is a project to devellop an interface which
>connects the expansion slot of the C64/128 directly with an ISA-slot of an
>PC. I finnished the theoretical part and I want to let you read it and to
>give comment on it. This project was also the reason why I asked those
>questions about the VIC and the SID. As it is meant to be published on my 
>site as well, it is in HTML.

Nice dream. But if you placing it under VIC (or SID) unused locations, you never
could gain 100% REU emulation. Right? Another problem is the complexity of design.
I believe most of us haven't enough time duplicate even the debugged one (or
better build it by own hands). Sad, but true, I also come into conclusion that
my project also will die soon, if I'll play too many time with its HW. Thus, I
returned to my first simple (not too fast) one, and improved it with some
new ideas. Then it could be used without opening the 64 itself and without 
filling EXPANSION port or making pass-thru slots. For interested ones, I'm
connected my C64/128 (in future C65:) user port with PC parallel port by simple
3-chip interface (okay, now 5 chips) and have nice results. I sent one to Marko,
but I told him not to spread the design itself because of low SW support (now).
OK! For less words, I will return with my Web Page addy soon. Thanks.

>As it is meant to be published on my site as well, it is in HTML.

Probably we have some browsers under hands, so http://... enough for us :-)


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