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I forked fromupstream to document my BIOS development inCPM_3_Custom_BIOS. My target is the addition of a 2nd serial interface via the I2Cport of the AVR chip. The serial module is inspired by theidea 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 viaMAKE.COM.Files are transfered between Linux and CP/M withlrzsz andXM.COM, using the xmodem protocol.

Current status:

• Original BIOS source code in Z80 syntax (*.MAC) builds a workingCPM3.SYS.
• MAKEFILE allows the faster build that translates only changed parts.
• CHARIO.MAC provides a dummyAUXIN (returnsEOF) andAUXOUT (kind of/dev/null).
• S220718-R290823_IOS-Z80-MBC2.ino provides I/O commands forAUXIN,AUXOUT,AUXSTAT andAUXCTRL.
• Makefile allows the compiling of the*.ino viaarduino-cli tool.

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 ...

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