On Sun, 5 Dec 1999, Nicolas Welte wrote:
> Then I found the file "8250-8050" on the 4040 side. Ken probably used it
> to format the 8050 disk, and it helped also for reading the disk. From
> now on the 8250 wouldn't report an error anymore when trying to read the
> 8050 disk and uni-copy happily copied the files on the disk.
>
> For those interested, here's the program:
>
> 10 open 15,8,15
> 20 print#15,"m-w"chr$(172)chr$(16)chr$(1)chr$(1)
> 30 print#15,"m-w"chr$(195)chr$(16)chr$(1)chr$(0)
> 40 print#15 ,"u9"
> 50 close 15
>
> For me it looks like two memory locations are changed an then the drive
> is warm started.
After doing a little searching of the drive memory of the 8050 and 8250, I
have figured out what's happening here.
First here is a list of the contents of relevant memory locations in the
drive (all in page 16):
8050 8250 Comment
172 1 2 Number of disk sides.
192 38 38 Track numbers for the
193 38 38 BAM sectors ant the first
194 39 38 directory sector.
195 0 38
196 0 39
197 0 0 Sector numbers for the
198 3 3 BAM sectors and the first
199 1 6 directory sector.
200 0 9
201 0 1
233 78 155 Total number of tracks + 1.
237 0 77 Tracks on side 0.
The program above sets the number of sides to 1, and truncates the BAM
sector list and then jumps to the NMI. Note: jumping to the reset would
undue the changes.
Changing some of the other values listed here may make this routine work
in other situations.
Just for fun, I put the 8250 values into an 8050 and formatted a disk.
It stopped with a read error on track 38 sector 0. When I examined the
disk, I found I had a disk with tracks 78-154. Apparently, It wrote both
sides to side 1, overwriting the side 0 format, and got a read error when
it tried to write the BAM on track 38, which no longer existed.
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