This does not apply to ROMs because the ROM is normally written by a different computer so datalines and Adresslines need to be in the correct order.
A17 and A18 are very high for 8 Bit computers who normally only have A0 to A15 giving 64K.
So with A16 being correct, this is 128K of continuous ROM. What size are Z88 ROMs normally?
If it's the Z88 itself then it just doesn't bother like with RAM.
I'm guessing that another issue with having the A17 and A18 address lines swapped (because they are tied to the external ROM slot #2) is that any external cards programmed by the swapped Z88 might not be readable by another Z88 that doesn't have the lines swapped?
I do however label A17 & A18 consistently with their actual positions on the motherboard near the card connector. Consequently the correct address lines are indeed linked to the flash memory chip at their expected pins. I can confirm that I have successfully flashed OZ 5.0 in place from OZ 4.7.1 without incident.
Well, I've spent hours today trying to get my Z88 to recognise my internal 512KB FLASH ROM and have contact traced it three times and re-wired the mod twice; now it looks more like your layout (my wires are now shorter which is good) however the Z88 still thinks it has an EPROM inside and not FLASH and so I can't do an in place upgrade.
I guess I'll just have to bite the bullet and buy a new SST brand FLASH ROM. I'll probably buy the same RAM IC that you used as well, then try the mod again when they arrive.
Really appreciate the help everyone!
I thought I'd leave a reply on here just so that others know that this post is still the best upgrade documentation to follow, and to say thank you to Jamie for documenting the process.
Glad there are now a good number of Z88s that have been upgraded without resorting to carving up their boards. May there be many more to come.