Thanks to the great help from Wayne Warthen I'm delighted to report that I how have the Z180 S100 board booting up signing on via its serial A port. Thanks Wayne.
I have use the suggested code Wayne put together. It's just a few lines long -- but critical lines. The problem was I was not having valid RAM.
With the equates its a bit long to list here. So I will add it as a text file.
The remaining challenge is to get the memory setup so the CPU sees 64K of RAM with just the lowest 4K of the ROM moved to E000-FFFFH in that RAM. This would mirror the configuration of our current Z80 S100 bus CPU boards. Having a simple monitor like this makes debugging S100 bus new hardware boards much simpler. Of course with 512K of ROM you can later add all the SC131 stuff and/or more.
OK for memory management Wayne has:-
; z180 MMU setup
out0 (z180_cbar),a ; setup for 32k/32k bank config
ld a,(1024 - 64) >> 2
out0 (z180_cbr),a ; common base = last (top) bank
If I understand that, the bottom 32k is the ROM and the top 32K is RAM.
We need to get things so me move the lowest 4K of ROM to that top RAM at E000H-FFFFH (easy), but them we need to release the bottom 32K of ROM so its all RAM.
This is possible see the attached manual page (Fig 23, Common 0).
The problem is I don't quite know how to do this. Suggestions guys..