1541 DriveMirror (was Re: Wanted: ultra-rare Commodore 64 stuff)

Ethan Dicks ethan.dicks at usap.gov
Tue Jan 1 05:18:05 CST 2008

On Tue, Jan 01, 2008 at 03:37:44AM -0600, Jim Brain wrote:
> Dan Gahlinger wrote:
> >I'm looking for something very rare on the commodore  64 (c64 or 64c) line 
> >of computers,
> >
> >it was called "drive mirror" for the 1541 disk drives
> >
> >it was basically an LCD display built into the drive that showed the track 
> >and sector values.

LCD?  I remember an LED track-only display.

> >I read a magazine article (or online) once that showed how to do the track 
> >and sector displays...

Any recollection where?

> I'm assuming a T&S display would have to intercept some RAM locations, 
> as the electronics do not have any idea of the T&S.  address 0x22 holds 
> track, while 0x4d holds next sector to read (0x4c holds last sector 
> read).  I'm assuming one would just wire up a 573 to each address, and 
> grab the data, converting it to decimal.
> 0x80 also states it is TRACK, with 0x81 being sector.  These may be the 
> bytes Drive Mirror was looking at, since they are so close together, it 
> would be relatively easy to decode them.

Sure... wouldn't even take a '688 or other large address decoder.  An
8-input NAND or two with an additional gate for 0x80 vs 0x81 for the
latch input.  Hex to 2-digit BCD might be a bit hairy in TTL, though.
Did the Drive Mirror use PALs/GALs or straight TTL?
> I've got some Atmel AVR code here that could possibly be persuaded to 
> "snoop" on the drive line and watch all the IEC commands, optionally 
> outputting them to an LCD.
> I remember the ad for Drive Mirror, but I never have seen one.

Any idea how it mounted?  Did you install flea clips?  Solder on wires?
Plug into the CPU socket?


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Ethan.Dicks at usap.gov            http://penguincentral.com/penguincentral.html

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