I forked from upstream to document my BIOS development in CPM_3_Custom_BIOS. My target is the addition of a 2nd serial interface via the I2C port of the AVR chip. The serial module is inspired by the idea of eightbitswide, but I'll implement it gapless into the BIOS as AUX device.
I edit the source code on my Debian Linux and build directly on the CP/M system via MAKE.COM.
Files are transfered between Linux and CP/M with lrzsz and XM.COM, using the xmodem protocol.
Current status:
- Original BIOS source code in Z80 syntax (
*.MAC) builds a workingCPM3.SYS. MAKEFILEallows the faster build that translates only changed parts.CHARIO.MACprovides a dummyAUXIN(returnsEOF) andAUXOUT(kind of/dev/null).S220718-R290823_IOS-Z80-MBC2.inoprovides I/O commands forAUXIN,AUXOUT,AUXSTATandAUXCTRL.Makefileallows the compiling of the*.inoviaarduino-clitool.
Next goal:
- Implementation of a simple I2C target on an Arduino Nano to test the signal flow, initially as bufferless AUXOUT without handshake signals.
Further steps:
- Add a serial buffer and handshake signals on the target.
- AUXIN ...
Original README file from upstream
The Z80-MBC2 is an easy to build Z80 SBC (Single Board Computer). It is the "evolution" of the Z80-MBC (https://hackaday.io/project/19000-a-4-4ics-z80-homemade-computer-on-breadboard), with a SD as "disk emulator" and with a 128KB banked RAM for CP/M 3 (but it can run CP/M 2.2, QP/M 2.71, UCSD Pascal and others).
It has an optional on board 16x GPIO expander, and uses common cheap add-on modules for the SD and the RTC options. It has an "Arduino heart" using an Atmega32A as EEPROM and "universal" I/O emulator (so a "legacy" EPROM programmer is not needed).
It is a complete development "ecosystem", and using the iLoad boot mode it is possible cross-compile, load and execute on the target an Assembler or C program (using the SDCC compiler) with a single command (like in the Arduino IDE).
Project page: https://hackaday.io/project/159973-z80-mbc2-4ics-homemade-z80-computer
Latest IOS revision: IOS S220718-R290823