[CCTALK] Commodore 1541 Drive

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Wed May 15 11:46:58 2002

--- Pat Finnegan <pat_at_purdueriots.com> wrote:
> I'm trying to get one, and wondering what success people have had with
> connecting them to a PC using "X-Cables" and "Star commander" to transfer
> data ( http://sta.c64.org/sc.html ).

I have a homemade cable that is the model *before* the X cables were
devised. I keep a 486 around for reading 1541 disks.

> Also, is there any chance of making
> a 1541 read an Apple ][ disk? I know they both use GCR encodings for
> their disks, and it'd be really useful if I could read disks on my PC.

Not as far as I know. I think the lowest bit density on the 1541
is identical to what the Apple ][ uses over the entire surface (it's
17 sectors of 256 bytes on the 1541, vs 16 on the Apple ][, but
due to header/trailer differences), but I do not recall a single
program or trick to read an Apple disk in a 1541.

I was a beta tester for the Spartan Mimic, the expensive and unpopular
Apple "emulator" for the C-64 (co-processor is more like it). One of
the boards that came in the box was a card that sat inside the 1541,
between the drive mech and the 1541 mainboard. It had lots of relays
and stole the drive mech out from under the 1541 board. That was
the only Commodore drive I ever saw read an Apple ][ disk, and it
still needed an Apple controller to do it (there was a 20-pin connector
on the Spartan drive board).

Among other differences (smart vs dumb peripherals), the 1541 depends
on a certain header design - there's an 8-input NAND hooked to a shift
register on the input side, and the Set Overflow pin of the 6502 on
the other. When a bunch of 1s go streaming past the head, this logic
kicks the processor out of a tight loop where it branches to itself
while the overflow bit is clear. This, coupled with precise timing,
lets the 6502 in the drive know when to grab the data from the sector
header. I can't describe how the Apple ][ state machine PROM works,
but it is its own flavor of beast, resembling nothing else in the
home-computer arena. I'm not surprised that nobody ever got things
to read in other brands of computer.

> Also, does anyone know anywhere I could get a Compaticard (and any
> necessary drivers to make it useful)? I've looked on ebay a few times now
> and still haven't seen one...

Can't help you there.

-ethan



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Received on Wed May 15 2002 - 11:46:58 BST

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