Use Case
Replacing the internal ROM with a 512KB Flash chip allows for the Z88 to be upgraded to a more modern OZ version without consuming a flash card in Slot 1.
However some useful Z88 software does not function on the newer OZ versions, since these authors deviated from the Cambridge developer guidelines. SpellMaster, and Vision2 VT100 terminal are two such applications. Using a Z88 as a portable serial terminal, with its full size keyboard, remains a useful proposition even today.
However once a Z88 had a Slot 0 flash modification performed, it could no longer run these useful applications… until now!
OZ Version Selection
One of the most cumbersome constraints of OZ 3.0 and earlier was the dependence on a RAM card in Slot 1 for Expanded mode, which Vision requires. By using OZ 4.0 on a Z88 with 512KB RAM and 512KB of flash in Slot 0 we can achieve a fully backward compatible Expanded machine without needing any other cards.
Tools to Bundle
XY-Modem - for fast file transfers over serial
FlashStore - for managing flash file storage
RomUpdate - for simple application ROM blowing to flash and to update OZ (to return to 4.7.1 or 5.0)
RomCombiner - for managing multiple application ROMs on flash
Installer - to install run application ROMs from RAM (no flash card needed)
After using OZ 4.7.1 or OZ 5.0 it's easy to forget just how irritating it can be returning to one of the stock versions. Simply transferring files is a chore, often painfully slow since EazyLink2 standalone is limited to 9600bps. However, Dennis Gröning's XY-Modem can achieve around a 10x speed improvement, explained in this guide.
Since my own updates in 2022/23, all of the essential flash tools above have been updated to add compatibility for newer flash memory types - so they remain current even running on old OZ versions.
ROM Modifications
By editing the card size in the Application Front DOR and the last application DOR in the OZ ROM image we can add extra applications to the Index. We can also fix several bugs in OZ 4.0 at the same time. Both processes are explained on Dennis Gröning's website.
As was done with OZ 4.3 onwards, we can add a file area to make use of the remaining flash space. We can pre-populate this with the BBC BASIC versions of Installer, RomCombiner, and RomUpdate. These have the advantage of being usable without needing to be blown to a card and, since we will be running OZ 4.0, their requirement for an Expanded Z88 will always be met (assuming a Slot 0 RAM upgrade).
Installer Constraints
Note that to use RAM apps, Installer will require a dedicated RAM card because OZ 4.0 is not capable of detecting applications installed to the RAM portion of a hybrid RAM/flash card, nor in Slot 0 RAM. Installer cannot in fact use hybrid card RAM but, even were it possible, OZ 4.0 would only evaluate the Front DOR at bank 63 at the top of the card (in flash), and that would contain no reference to any RAM app. The newer OZ versions have been modified to also scan bank 31 of hybrid cards (top of RAM).
Patching Vision for Slot 0
Vision was sold on a 32KB EPROM. It also required an Expanded Z88, which at the time would have mandated a RAM card in Slot 1. Consequently its bank switching code assumes it will only ever run from Slots 2 or 3. The quirk of
Downgrade ROM Manifest
CFG.V3 ; OZ ROM for slot 0 and total of 16 banks to update. OZ.0,16 ; Bank file, CRC, destination bank in slot 0. "ozs0-400.32",$9de67a39,$00 "ozs0-400.33",$1d32d297,$01 "ozs0-400.34",$65ed5623,$02 "ozs0-400.35",$e2e022c6,$03 "ozs0-400.36",$8758704a,$04 "ozs0-400.37",$b860cf23,$05 "ozs0-400.38",$d3104e3f,$06 "ozs0-400.39",$5c5de229,$07 "flashst-197.40",$88ce8262,$08 "zip-xymodem.41",$83cf1ae5,$09 "vision2-206.42",$fd18a731,$0a "vision2-206.43",$71ee7ae3,$0b "file-area.44",$1ec9d2c1,$0c "file-area.45",$6666ce43,$0d "file-area.46",$420c789c,$0e "ozs0-400.63",$3d6adf54,$1f
To Do
There is over 256KB remaining on the file area - just enough to accommodate SpellMaster. It needs some disassembly to locate and patch its bank switching code.