PET schematics bugs

From: Andre Fachat (
Date: 1998-05-07 22:11:25

Hi Marko,

it is interesting what CBM sold as schematics :-)

The 2001 schemtics (with static RAMs and 2k ROMs) have a bug, 
i.e. the ones with the 2316 ROMs. 
Every two of them are connected to exactly the same lines, even 
select lines. This is probably a transcription bug, as the 6540 2k ROM
from Commodore had other select lines, such that one could
connect BA11 (switches between the upper and lower half of a 4k page)
to either /CS3 or CS1 for upper and lower half ROMs.
So all ROMs were connected to BA11.
The 2316 don't have this line, but still all are connected
to BA11, and all at the same pin, CS2. Instead the lower half ROMs
should be connected to /BA11

One more comment to the 2001N schematics. One might wonder why the 
ROM for $E*** is selected with /SELE only while the I/O is selected
with /SELE and x8xx. This would suggest that in $E8** both would be
selected and drive the bus, which would fail. 
But: The 2316 has a low-active select line at pin 18, where the 
2332 has A11. But only a A11 is written in the schematics, so 
you have to guess that the IC (if and only if 2k) is selected only
when A11 is low, i.e. $E000-$E7FF.
And you should better not put a 4k ROM in there :-)

Do you put that somewhere in the READMEs or should I put that
to my PETindex?


BTW: did the CBM-II stuff help?
Email address may be invalid. Use "fachat AT physik DOT tu-chemnitz DOT de"
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Andre Fachat, Institute of physics, Technische Universität Chemnitz, FRG

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