[Coco] Re: Oddball disk format question

[Torsten Dittel]

Gosh, I don't find my "Scheibenkleister II" book.

I've been digging in memory and I remember something concerning the CRC
command: If you WRITETRACK something like

$F5 $F5 $F5 $F7 $F7
you'll get something like
$?? $A1 $A1 CRC CRC $F7(!)
and ****NOT***
$?? $A1 $A1 CRC CRC CRC CRC(!)
(this should be a controller "bug")

Maybe this hint helps.

Another trick I remember: There are some "killer" bit patterns, like $00
$29 $F5 wich will sync the READTRACK without producing $A1. You can put
some reproducable bytes after that sequence, but it's difficult to write
that if you don't now the trick and where to place it. You can even
create some "deadly" combinations of both tricks like $00 $29 $F5 $F7
$F7 ...

However, I don't remember exactly what exactly was going on. There were
further tricks writing "unvalid" address marks which will interpreted
correctly and so on because the controller is only using the first LSBs
of these bytes.

I knew so much about this stuff but this is 20 years ago. My memory is
like a black hole....

CU
Torsten