commodore 64/128 question
brain at jbrain.com
Mon Sep 4 15:39:00 CDT 2006
Roy J. Tellason wrote:
> Oh really? I was wondering what they were trying to do there. I was also of
> the impression that the +4 was supposed to be a replacement for the c64, and
> that the c16 (which I think I may have seen _one_ of perhaps) was supposed to
> replace the vic20. But I'm not really sure.
Originally, it was designed to replace the C116, to hit the TS1000 price
point. Jack wanted a CBM in every house. It was designed in Japan, and
eventually mutated into the C116. For the same price as Clive's TS1K,
it had color and ran a bit faster.
Then, and reports vary as to why, CBM tried to beef it up into an entire
product line. It was designed for absolute low parts count (the design
puts VIC-like sound back in the video, it lacks sprites, etc.) The
CV364 (with the speech synthesizer) would be the top end, with the 264
coming in second. Cameron can provide more detail on when the C16 (116
spec in a VIC/64 case) was added, I think it came later in the process.
In any case, they they then recruited Jim Butterfield to intro the units
at CES 1984. Jack told me he went to the prep meeting, and saw the
machines. He thought they were all nice to fit below the 64 in the
product line. They then informed him that they didn;t want to
cannibalize 64 sales, so they were positioning the +4 series as a
premium business product. Jim thought that was a dumb idea. It tanked,
as it should have.
Herd relates going around during the 84 show and vendors were yelling at
him about the units being incompatible. He assured them not too worry
about porting SW to the unit, as it would die. This is why he fought
hard for the C128 to be compatible with "something"
And the little C116 that originally held so much promise? A small
production was dumped in Japan, where they were not received all that
well. Mine is a prototype unit, which is why it is NTSC. Either
Cameron or Bo Zimmerman has a production unit, which I think is PAL.
> I read somewhere that the CP/M cartridge never actually worked all that well.
> If it worked at all.
Correct. Bil Herd notes that the design didn;t fully tristate the
busses, which it needs to do for the VIC to work.
> I have the 64's service manual around here someplace, and maybe I should look
> at the differences between the various boards, I don't remember anything in
> particular there that would account for this. I do remember a couple of
> lines of that port being labeled "Z80" and "DMA", which I never saw anything
Bil hangs out in comp.sys.amiga.* at times, maybe you can email him.
I've heard from numerous folks that on early boards work, but I never
cared enough to determine why.
> I also have the 128 manual on hand as well, but never really dug into the
> workings of that MMU chip. As a service center and wanting to have a
> complete set of spares on hand I did get a hold of some of those, and some
> of the PLA chips that were used in the 128, as well as a number of the parts
> peculiar to the 1571, and ended up never using any of them. I don't know if
> they'd be useful in anything else offhand.
Well, technically, I'm talking about the ROMH, ROML, EXROM, etc. lines
of the 64, which would change the memory map. The IC controlling them
is the PLA. Calling it an MMU (given the current usage of the term) is
probably misleading. The C128 has a better attempt at an MMU, where
memory can be programmatically remapped. IN essence, the EXROM, ROMH,
ROML were only intended to be changed upon powerup, but on the 64, they
could be changed at any time to affect the memory map. Some carts would
use this to an advantage. The C128 had issues with this usage of the lines.
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