[Coco] Copying over an IO ERROR

[Darren A]

On Wed, Feb 4, 2015 at 8:39 PM, Arthur Flexser wrote:

> Out of curiosity, Darren, what does a "true" address mark consist of?
>
>
In MFM encoding, an address mark normally consists of three "sync bytes"
followed by a mark byte ranging from $F8 to $FE.  The sync bytes can be
either an $A1 byte with missing clock between bits 4 and 5, or a $C2 byte
with missing clock between bits 3 and 4.  It is the sync bytes which
actually trigger the address mark detector.

More details including info about the Read Track problem can be found at:
<http://info-coach.fr/atari/hardware/FD-Hard.php#FDC_Address_Mark_Detector>

- Darren