Yet another home-brew z80 system
This project has diverged a lot from my original plan to build a
from-scratch portable Z80 system. I may yet do that. Meanwhile I
have an RC2014 system running happily which is very flaky.
- FPGA_VGA - RC2014 board hosting an FPGA module for VGA text video
- FPGA_firmware - firmware (Xilinx Vivado) for above
- Keyboard - 60% keyboard with serial output
- AVR_Code - AVR firmware for keyboard
After having fun with an RC2014 system for a bit, I found it to be too flaky for serious use. Not really interested in debugging it now.
2023 Proposed changes:
- Consider ECB SBC compatible design, but with Z80 CTC, DART, PIO instead of the Intel ones
- Add an IDE interface. Seems as if an 8255 is a winner for this
- Maybe an ICOM Floppy interface, another 8255?
- Connect the CTC TO/TRG pins to a header (only)
- Add a 4.9152 osc and 74HC4040 as a simple baud rate generator
- Change the CPU clock to 4/8 MHz
- Add a network interface with ENC28J60 (see e.g. http://tuxgraphics.org/electronics/200905/embedded-tcp-ip-stack.shtml)
I'm starting (slowly, for now) on a home-brew Z80 general-purpose computer. I'm not very interested in the 8-bit gaming or retro-Apple-Amiga world, but basically a re-creation of my development system in 1984 or so. It had a Z80B, I think 192k or 256k RAM, a bunch of EEPROM configured as a read-only disk, 24x80 video with attributes or color and a nice double-density floppy disk interface with dual 3.5" floppy drives. I'd like to enhance it with decent-quality graphics, maybe 640x480 or 800x600 16-color (from a palette). Not sure yet about whether I want to fuss with a real floppy system. If it could be portable, as in a laptop, that would be cool.
This will be derived from my https://github.com/eshazen/retro-25 project. Tentative feature list:
- Z80 CPU, DART, PIO
- AT28C256 32Kx8 EEPROM
- AS6C4008 512Kx8 SRAM
- Clocks: 8MHz osc /2 => 4MHz CPU clock or maybe faster
- Clocks: 1.8432MHz / 12 => 16X 9600 clock
- MAX232 or equiv; DB-25 for RS-232
Targeting at least 24x80 or greater VGA text with 640x480 pixel resolution. Eventually would like an in-period solution, maybe an MC6845. First version will use a Basys-3 FPGA board with this opencores VHDL code: https://opencores.org/projects/interface_vga80x40. I bought a 5.7 in 640x480 LCD: eBay. It has an annoying 0.5mm pitch flexi connector so I made a breakout board:
