UPDATE 24/06/2023 - I ran out of v2.1 parts so took the opportunity to make a board update to v2.2, (3d image in last picture) and I have just ordered 10 sets of parts, should be with me late July. The v2.2 change was to add a RESET in/out connector so that the MZ-80A RESET switch also resets the ROM paging latches - occasional CPM crash would leave the registers pointing to a ROM disk page and so wouldn't reset without power cycling.

Overview

The Sharp MZ80A came with 48K RAM and 4K ROM and apart from the option to add a 2K User RAM/ROM and a 4K Floppy Drive ROM, there was no further possibility to expand the machine memory capabilities at the hardware level and thus no additional firmware could be added for use at power-on. Add-ons had to rely on loading control firmware into RAM via tape or floppy, thus depleting valuable application space. Some machines of the same era utilised a scheme called 'banking' whereby much larger memories would occupy a smaller block within the CPU address space and be selected according to features required and hardware attached. The BBC Micro was such a machine with up to 16 banks of 16Kb, it made the machine much more useable.

This upgrade board goes a stage further, not only allowing for banked ROM images to be added to the MZ-80A, it also allows for application storage in spare ROM space, adds additional banked RAM (512KB in 2K pages) and additionally, a hardware or software SPI interface driving an SDHC card.

New monitor firmware has been written to allow full use of this upgrade, allowing indexed search and execution of files in ROM or SD card, new monitor commands and CP/M v2.2 running in 40 column mode, or 80 column mode if a 40/80 column adapter has been installed.

All the hardware and firmware is Open Source including CP/M v2.2 with custom BIOS.

Installation

Installation is simply a matter of removing the original Monitor ROM and any ROM/RAM IC in the User ROM socket then inserting this card onto the Monitor ROM/User ROM sockets. Power on will see the familiar SA-1510 banner appended with '+RFS'. Typing 'h' will provide help on available commands which can also be seen in this list.

This board has been installed in multiple MZ-80A computers and I've recently acquired an MZ-1200 which is almost identical to the MZ-80A apart from needing to install a User ROM socket. I will soon update the firmware so that it works with the SP-1002 monitor.

Please see my website for full Rom Disk project detail, Rom Filing System firmware or github for full source code.

Whats Included

1 x Rom Disk v2.1 Upgrade board, includes 3x512KB FlashRAM and 1x512KB Static RAM IC's, SD Card interface, 16GB SD Card pre-loaded with Sharp Software, 4x12 way IC Socket extender strips (to increase height above mainboard if required).

All documentation, design files, software, schematics are available online. The designs for this adapter are freely available on github for non-commercial purposes should you wish to source the parts and build the adapter yourself.