Re: 8250 help needed

From: Andre Fachat (
Date: 1999-06-05 12:21:13

Nicolas Welte wrote:
> Maybe I could, but it makes no sense: I have a box of disks and I don't
> know which ones are single and which ones are double sided. I had to
> modify it in a way that it detects the disk type and then uses 77 or 144
> tracks. 

So you´re probably best of with a program that reads sector 38/3 (or
so, the second BAM block) and sees whether it points to track 38 
(8250 format) or 39 (8050 format), and depending on that resets the 
drive appropriately.

> What makes you think so? Today I also got a SFD1001 and I also thought
> that it's misaligned: It can't read the disks that came with the 8250.
> But it formats disks just fine, and reads them back in. BUT: The 8250
> also reads this disk (at least the dir). And even a freshly 8250
> formatted disk won't work in the SFD. This is very strange...

Yes indeed. As I said, I cannot format disks at the moment, so 
I cannot test much. My single 8050 disk is read in the 8250 
without problem in both drives, but the 1001 chokes on it.

> So far it worked fine for me with the cheaper disks. I have some QD
> disks (they don't say QD, but 2S/2D 96tpi, which should be the same)
> which I got from the University trash, and they're formatted in CBM DOS
> 1 format (670 blocks free)! If you like some to make experiments with
> ;-)

If you could part with two or three, that would be nice!
Somewhere I have a patched VC1541 ROM where I tried to 
make it use the DOS 1 format - I tried it with my 6502 emulator
from my selfbuilt computer, but don´t remember the outcome.

That reminds me: Did anyone try to replace the 1MHz I/O and CPU
with 2MHz components and patched the ROM to work in 2 MHz?
I once tried it (with an IEEE488 interface, so no serial IEC 
timing troubles) but did not succeed...


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