A Lockdown-inspired Junkbox Z80 System
Designed and built from on-hand parts in early 2020, COOF-80 (stylized in hexadecimal compatible as C00F-80) is Z80 system implementation that would be relatively sophisticated if it was 1980. Unfortunately it is not 1980, so it's more of an example of the most basic level of computing and a fun toy model computer to play with. Includes a simple and probably buggy interactive ROM monitor.
- Built using advanced perfboard technology
- Z80 microprocessor running at up to 4MHz
- Precision crystal oscillator with selectable clock divide factors (÷1, ÷2, ÷4)
- 8KB EPROM
- 24KB fast static RAM
- High-speed 16C550 UART for serial communication
- Byte-wide bank of blinkenlights for efficient human interfacing
- /Design
- C80-schematic.pdf
- C80-schematic.png
- Schematic in PDF and PNG format
- COOF-80/
- KICAD 6 project
- Currently there is no PCB design
- /ASM
- MAKE.BAT
- Builds included files using TASM32 (not included, place in path)
- Generated binary images in intel hex format are placed in ./bin/
- blinkenlights.asm
- Basically hello world
- Implements ping-pong scrolling LED effect suitable for installation on the grille of a 1982 Pontiac Trans-Am
- z80monitor.asm
- ROM monitor for interactive development and debugging
- Uses UART interface for console
- MAKE.BAT
- /GAL
- z80logic.PLD
- z80logic.jed
- PLD equations and synthesized JEDEC file for system glue logic GAL
- 16C550.PLD
- 16C550.jed
- PLD equations and synthesized JEDEC file for UART glue logic GAL
- z80logic.ods
- Prettified truth table of system glue logic in LibreOffice Calc format
- Firmware was built using TASM32 ('Telemark Assembler', not to be confused with 'Turbo Assembler'), a vintage freeware assembler for Windows (and apparently Linux). Source may or may not be directly compatible with other assemblers.
- PLD code was built using
Atmel'sMicrochip's WinCUPL - ASM80 is quite handy for development
- As is ZEMU by Joe Moore
d[ump] <hexaddr> <hexlen>
Dump <hexlen> bytes memory starting at <hexaddr>
x[ecute] <hexaddr>
Jump to <hexaddr> and execute
c[all] <hexaddr>
Call <hexaddr> and return to monitor
f[ill] <hexaddr> <hexlen> <hexval>
Fill <hexlen> bytes starting at <hexaddr> with <hexval>
:ihxstring
Load Intel hex string into memory
w[rite] <hexval> <hexaddr>
Write <hexval> to memory location <hexaddr>
i[nput] <hexport>
Read <hexport> and print the value (high order byte ignored)
o[utput] <hexport> <hexval>
Write <hexval> to <hexport> (high order byte ignored)
Call IDs:
0x00 - NOP
0x01 - Get character from UART, returned in A
0x02 - Send character in A to UART
0x03 - Send zero-terminated string pointed to by HL to UART
0x04 - Split rxbuf and place in argbuf
0x05 - Convert byte in A to ASCII hex, leave two chars in HL
0x06 - Convert two ASCII chars in HL to byte, leave byte in A
0x07 - Delay number of loops specified by HL
0x08 - Get argbuf address and return it in HL
0x09 - Get rxbuf address and return it in HL
0x0A - Get substring index in A from argbuf, return address in IX
Calling convention:
- Push call number on stack
- Load registers as appropriate for the API call being used
- Execute RST 08h
- ISA Bus
- I've attempted to interface an ISA MDA card with some degree of success. I can configure the CRTC and get it into a mode that can be fed into a VGA monitor, but memory writes to the framebuffer are unreliable and I'm not sure why. May revisit this eventually when I get a 16 bit Salae Logic and can better watch the bus. Source for configuring the CRTC is included in ASM/extra/mda.asm, and is intended to be pasted into the monitor using the Intel hex handler. Hardware for doing this is undocumented at the moment, but the short of it is most of the signals just need to be connected since ISA is basically an 8088 bus and the Z80 is fairly close to begin with being a conceptual relative of the 8080.