RE: Who owns a 8050/8250 with tandon drives?

From: Martin Hoffmann-Vetter <>
Date: Wed, 30 Apr 2014 15:46:05 +0200
Message-ID: <003e01cf647a$893da520$>

> 2040:  You have the 901466-01 image.  There is also a 901466-02.  Is
> it the same?

Yes, the rom content from 901466-01 and 901466-02 are the same. At this time
i don't compare the complete logic to decode the addresses. I've discussed
with Wolfgang Moser about there two part numbers, too. But there isn't a

> 251474-01b:  This is the same as the DOS 2.7 Tandon. The 74LS06 hex
> inverter is probably there to provide the logic necessary to make a 4K
> EPROM appear as a 1K EPROM to the 6530.  There isn't space in the
> 6530's address space for a 4K ROM.

The 251474-01b is a 2k eprom. The used content is the first half. The second
half isn't accessable and filled with $aa. The inverter is used to invert
the phi2 signal to the second enable input. You remember, the 8250 have two
cpus on one memory bus. See the schematics from the sfd 1001. There is an
other adapter, too.

> 2.7b DOS and fdc are a version of Speeddos. The fdc has only 55
> differences with the Speeddos fdc.  The DOS has only 251 differences
> out of 16K,  99 differences if you don't count different fill byte.
> The message area of the ROM contains the message "DOS SOFTWARE" that
> isn't in Commodore DOS.  There are also two additional commands in
> the command list, "O" and "?".

Yes, that's alright. The Speedos (only one "d") is an 3rd party product. But
at this time it's the only known extension fur the commodore (dual-)
floppies with two cpus.

The Speedos expand the cbm dos with some features. To control there new
features the new commands are implementated. For more informtion you find
the handbook (in german) at

Btw, at this time a analyse the bus controller roms. So i found we have the
DOS 1.2 with the roms 901468-06 and 901468-07. The next version is DOS 2.1
(!) with the roms 901468-11, 901468-12 and 901468-13. Why is this version
2.1? Look into the source code from this rom called You find the
reference to that roms! So the 901468-14, 901468-15 and 901468-16 is an
revised version 2.1. I would say, it exists an DOS 2.0 with the roms
901468-08, 901468-09 and 901468-10. But at this time the DOS 1.0 and 2.0 are

Look at the DOS 2.5. There are two known revisions. The first one is rom
901482-03 and 901482-04. The second one is 901482-06 and 901482-07. Both
version have the code at the same addresses. No movement is detected. So the
901482-06 and 901482-07 is an revised version from 901482-03 and 901482-04.
But if you look at the "The Complete Commodore Inner Space Anthology" you
will find a 8050 disk rom map. These labels are not useable for both rom
versions. The referenced routine "AUTOIT" was removed and all code behind
change the addresses! So it must be exists an early version 2.5 with the
roms 901482-01 and 901482-02! This first reevision of a DOS 2.5 is missing,

Who knows anything about this missing version?


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Received on 2014-04-30 14:05:01

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