Re: CBM secrets

From: Andre Fachat (
Date: 1999-06-01 14:49:36

Also the SuperPET was known as "MMF 9000" in Europe,
a "MicroMainFrame"

Also I should probably say something about the PET 8096/8296 models,
at least from a technical point of view.

The 8096 basically is an 8032 with a 64k expansion board. 
The expansion RAM could replace the area from $8000-$bfff and
$c000-$ffff with two expansion banks each.
The expansion is controlled by a write-only register at $fff0.
This register allows to enable/disable the RAM expansion, and to 
separately select the RAM bank for each of the two address ranges.
Also it was possible to separately write-protect the expansion RAM in
the two address ranges.
Screen and I/O could be made peek-through.
So this is a perfect expansion to test new ROMs for example, and
so probably this expansion originated in a CBM-internal test board.

CBM then invented a brushed-up BASIC, called the "LOS-96" operating
system, while still keeping compatibility with the original 8032
due to the still installed old ROMs.
The LOS-96 docs say that the OS resides in the lower 32k, while
the first 32k expansion is used for BASIC program and stack area,
and the second for variables, arrays and strings.
Unfortunately I only know of the German docs to this expansion
(on the PETindex pages).

After CBM introduced the "slim-line" or "wind-channel-proved"
(as we used to say) casings of the separate keyboard model,
they found that the old universal board for the 8032 did not
fit into the new case. Because the new board was not ready,
they somehow fitted the old board in the new case with 
cables running from the board to the connectors at the back side
(and front side for the keyboard) of the case. The 8032-SK was born.

The new board that CBM then introduced is not very well known.
It finally fit into the rounded, separate keyboard cases, 
removing the need for the extra cables of the 8032-SK.
It is mostly an 8032 board with builtin 8096 expansion. 
Although the board has 128k (of which 96k are used like in the 8096)
only a little more than 96k can be used. 
The missing 32k are "under" the ROM area like in the C64. But only part
of it can be accessed. The part from $8000 replaces
the separate video RAM chip of the old PET. 
In fact the addressable area of the CRTC has been increased
to 8k. Thus even without special tricks a second screen can be 
used in the $8800 area by setting the CRTC screen start address. 
The area at $9xxx and $axxx can be made accessible as RAM by
setting jumpers on the board.
The board is also designed to be used for 80 and 40 columns 
machines, with or without RAM expansion. However, I have not
heard of any other machine besides the 8296 using this board.

A picture of the 8296-D, that has a built-in 8250-LP (low profile)
dual disk drive can be seen in my gallery
(scroll down to the bottom)


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Andre Fachat, Institute of physics, Technische Universität Chemnitz, FRG
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