In my last post I introduced Guus Assmann’s SBC-V20 board, here is his SBC-Z80 version whose design files can be downloaded here.
Guus’ SBC-Z80 is built upon the just4fun @hackaday project 159973 Z80-MBC2: a 4 ICs homebrew Z80 computer applied to the SBC-85 backplane. Like the SBC-V20 project, an Atmel Mega32A microcontroller is the system workhorse providing ROM and I/O which includes an I2C port that communicates with a Microchip MCP23017 port expander.
The SBC-Z80 begins with the original SBC-85 backplane pinout and has further claimed a handful of previously unused pins HALT*, WAIT*, RFSH*, INT*, IORQ*, BUSACK*, and BUSRQ*). Like the original SBC-85 CPU board, the SBC-Z80 has a DB9 serial port with a MAX232 to generate true RS232 signal levels but it also brings off board the raw Mega32A signal levels for use with one of those handy TTL/CMOS to USB serial port adapters. Two of Guus’ completed boards are shown in the photograph, the one on the left has a micro SD and real time clock (via I2C) installed and a cable to a terminal board.
Primary components:
- Z80 CMOS CPU
- Atmel Mega 32A MCU
- 551001 (128KB) w/ DS1210 RAM controller
- MCP23017 port expander (I2C)
- MAX232 TTL / RS232 Level Shifter
I/O:
- SD Module with virtual disk capability
- Real Time clock Module
- 2x 8-bit I/O Expansion
- 115K RS232 Serial Port (with CMOS level header)
- ISP for programming the Mega32A
- 120 pin backplane (à la SBC-85)
Guus’s project package including the assembly manual, BOM, schematic, and KiCAD source files, and Gerber build files are available here (link). Software and more description is on Hackaday under the base design by just4fun @hackaday project Z80-MBC2: a 4 ICs homebrew Z80 computer (link). I will leave it up to Guus to let us know how compatible the SBC-V20 and SBC-Z80 boards are with the other SBC-85 expansion cards. For questions regarding Guus’ SBC-V20, leave a comment for Guus or send me an email on my contact page and I will forward it to him so you can communicate directly.