Re: Apple II Drive reads CBM disk?

[Linards Ticmanis <ticmanis@gmx.de>]

Michael J. Mahon wrote:
> Jack Tseng wrote:
>> you know both commodore 1541 and Apple II Disk drive are using a GCR
>> encoding scheme. I am wondering if 1541 can read Apple II disk ? and
>> Apple
>> II disk drive can read CBM formatted?

> Since the clocking and coding schemes are quite different, I don't
> think this works.

Indeed it is the clock that poses the biggest problem. The CBM drives
use four different bit clock speeds, but none of them is identical to
the one Apple Disk II bit clock speed. This is probably an
insurmountable problem unless either system is physically modified in
some way.

> Atari and CBM drives actually contain all the reading logic in the
> drive firmware (which can be reloaded by special utilities), so the
> situation is quite different from the Apple II drive, which is directly
> controlled by the Apple's 6502 in combination with a data separator
> state machine on the Disk ][ Controller card.

As the CBM drives also use a user-programmable 6502 and a state machine
internally, the difference in this respect is not quite as large as it
seems. Though the Apple state machine has the added requirement that
every byte start with a 1 (unless you go out of your way). The CBM
drives don't require that.

But given the clock incompatibility, this point is moot.
-- 
Linards