Hardware Overview

The system comprises a main, standalone CPU board and two optional I/O cards. All the board designs are open source and available on Open Source Hardware Lab.

There's a lot of details on the various boards on that link, this repo primarily deals with the software. As an overview of what the system provides:

Main CPU board

• Z80 clocked at 14.74MHz
• 512K SRAM + 512K Flash memory in 16K pages and 4M address range
• SIO/0 dual UART (can use SIO/2)
• Z80 CTC
• SD Card interface. Pins suitable for the breakout board I have.
• Second SD Card interface (not currently supported in the softare). Allows two cards but more importantly easy copying between them for cloning. The second connector could also be used for any SPI peripheral with suitable software.
• Exported SPI interface. Includes two spare device select lines, also exported, allowing connection to external SPI devices
• DS1704+ real time clock with battery backup
• i2c interface (used for the clock and available on headers to connect external devices)
• A 60 pin expansion connector with exports the 22bit extended address bus (4MB address space)

Video Card

An 8 Bit memory mapped, character based monochrome video card. Similar to many 70's and early 80's computers like the Commodore Pet, Sharp MZ80K and TRS80. Main features are:

• 640x480 display
• 80 characters per row
• 30 rows
• 8x16 pixels per character
• Software defined character set.

Parallel I/O Board

The card is primarily provides parallel I/O but also includes a simple sound generator. Features:

• Z80 PIO dual port controller for general use
• Z80 PIO port A can optionally be used to drive a dual joystick interface (the port can be general I/O or joystick, not both!)
• Separate parallel keyboard interface. Rather than design a new keyboard I've chosen to use the brilliant Omega MSX keyboard. The keyboard connector on this board should directly connect to the Omega keyboard.
• Single channel sound chip SN76489