1 Jan
2008
1 Jan
'08
1:37 a.m.
Dan Gahlinger wrote:
Yeah, I've tried the commodore forums, for sale,
craigslist, etc. no luck
I thought I'd try my luck here, no harm I think.
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.
it also had a half-track indicator and a "density" indicator as well.
I read a magazine article (or online) once that showed how to do the track and sector
displays, but never had any info about the more interesting parts - the half-track and the
density display.
PORTB of the 6522 (the one servicing the drive mech, @ 0x1c00-0x1c0e)
PORTB:1-0 shows half track: BIT 0 = HALF TRACK STATUS
PORTB:6:5 shows density: 0-3 density
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. But, that assumes things use
the std DOS. IN a custom DOS, all bets would be off.
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.
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.
Jim