Commodore 1520 Plotter

I have one too, and as you may have guessed, I hacked it a bit. I bought the Technical manual from Sharp (mise is a PC1500 rather than a PC2), which geve ,me schematics, the instruction set, and useful ROM calls. It has a nice standard-ish expansion bus (16 parallel address lines, 8 parallel data lines, etc), so homebrew hardware hacks are certainly possible. I bolted a board to the bottom of my CE150 (and covered it with a custom-made plastic case) containng some 6364 RAM chips. I think I mapped 16K into the 'normal' address sapce for program and data storage and 8K into the secondtay space (accessible by PEEK# and POKE# IIRC) which can only be used for data. The HP71B is a much nicer machine, but a lot more expensive back then, and the techncial docs were out of this world (I think a comp[lete IDS cost more than the machine!). Of course the HP documentation was excellent and included full commented ROM source, but... (I now have it, BTW...). And the HP71 bus is nothing short of strange... -tony