[Coco] high density floppy controller mods

Brian Blake random_rodder at yahoo.com
Fri Aug 4 17:36:32 EDT 2006

Mike, you can get to them from coco3.com.

Mike Pepe <lamune at doki-doki.net> wrote:  Warren Hoslet wrote:

> -
> The extra gaps required for the additional 18 sectors may make things 
> pretty tight. Isn't that why PC disks went to 512 bytes per sector (to 
> double the data bytes per-track without increasing the sector count)?
> In any event, to modify Disk Basic 1.1 (2.1) to format more 
> sectors-per-track, you need to poke the new sector count into the 
> following addresses:
> $D5B6 $D5B8 $D5C5 $D5C9 $D5D2 $D67B $D6BC
> Also note that the DSKINI routine will only check to make sure that 
> there is enough unreserved memory available in the 32K Basic RAM to 
> format the standard 18 sector track.
> If you want to allow the DSKI$ and DSKO$ commands to be able to read and 
> write to the higher sector numbers, then you should poke the new sector 
> count minus one into location $D540.
> DISCLAIMER: I have never actually tested this, so I can't gaurantee that 
> these are the ONLY changes required. You should check out the Disk Basic 
> Unravelled book to learn more about the ROM routines.

Hi Warren,

I poked 36 into all those addresses and successfully formatted a disk. 
DIR returns a blank directory.

The smaller sector size does mean more overhead when compared with a PC 
1.44MB disk, but the spec allows for sectors as small as 128 bytes. So, 
there shouldn't be an issue. Also we know the mod on the old 26-3022 
controller works.

I remember hearing that the unraveled books were available for download 
as a PDF, but I haven't come across them yet. Got a url for me?



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