Yes, the Z80 is not yet hooked up, at all.

Speaking of which, rfka01: do you have the original document that the "PC100 SYSTEM SPECIFICATION" is scanned from? The PDF has a washed-out stripe down the middle of page 25 which obfuscates some of the details of how the Z80 side works. Is it possible to get that rescanned?

ETA: L_N: the aforementioned page 25 tells (some of) the tale. The default bootup mode is "Z flip", where Z80 0x0000 is 8088 0x8000, and indeed if you boot the driver right now a working Z80 image is stored at 0x8000.

I don't understand how the 8088 holds/resets the Z80 prior to that image being present though. I/O port 0 on both CPUs is a latch and interrupt going to the other CPU, but I don't see anything that would cause a reset. Both IRQ and NMI on the Z80 image at 0x8000 echo whatever they see back through the latch and then HALT.

ETA 2: the latch interrupt is actually RST 30, which thins the plot a little (the code that jumps to appears to copy the RAM around a bit and turn off Z-flip), so that may be all that's necessary to boot the Z80.

Last edited by R. Belmont; 05/06/12 02:28 AM.