Amstrad PCW 8256 and 3.5 DS2D Drives
cclist at sydex.com
Tue Jul 10 12:21:24 CDT 2007
I recently picked up an Amstrad 8256 for its floppy drive (Hint:
replace the drive belt with a cheap polyurethane "elastiband" type of
"rubber" band. It works great.) That left me with a machine that
would either hit the recyclers or that I could keep around.
When I looked at the basic box--4MHz Z80, graphics, 512K of RAM...I
couldn't bear to toss it out without at least playing with it a bit.
I installed a Teac FD235F 720K drive in place of the original one and
then contemplated what I was going to do for a boot diskette. None
came with the machine.
Digging through my collection turned up a 3.5" CP/M 3.0 boot diskette
for a PCW 9512 (DisKit), but simply trying to boot from it got me
nowhere. (Beep Beep Beep). I found that the checksum of the boot
sector identified the target boot machine. My sample checksummed to
0x01, where my documentation said that the PCW 8256 required a
checksum of 0xff. Decrementing the "fixup byte" at offset 0x0f in
the boot sector by 3 from 0xD1 to 0xCF did the trick. The lowly
Joyce now boots CP/M. I've not seen this trick documented, so I
thought I'd report it here. The easiest thing would have been to
change the boot ROM code, but that appears to be buried in a gate
array and not a regular EPROM.
I note that the PCW uses the RST 7 vector for interrupts, which
conflicts with the breakpoint interrupt used by DDT and ZSID.
Fortunately, there appears to be a patch for that.
While it might be fun to get the PCW to run MP/M II, my interest has
waned a bit, so the thing will now go back onto the shelf. Without a
regular printer or serial port, an anemic PSU and a horrible
keyboard, it's going to be of limited utility anyway--for now.
More information about the cctalk