Amstrad PCW 8256 and 3.5 DS2D Drives

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. Cheers, Chuck