Elwro 800 Junior uses two SN74S474 512x8 PROMs as IO and memory address decoders. These PROMs are increasingly difficult to obtain (and program), this project provides a GAL16V8-based plug-in replacement for both address decoders.
Note: there is another version using ATF1502ASL CPLDs in TQFP-44, if you prefer SMD devices and JTAG programming :)
Hardware files:
- pcb - schematic/PCB project in KiCAD 8 format
- PDF schematics - color and black&white
- interactive BOM file (you have to download it and open locally)
- Gerber files (in a jlcpcb-compatible ZIP format):
- addr_dec_gal.zip - single PCB
- addr_dec_gal_panel.zip - two PCBs panelized
PLD sources:
- io - source and JEDEC file for I/O address decoder
- mem - source and JEDEC file for memory address decoder
Both decoders have been verified by comparing them against PROM dumps and tested to ensure they function correctly in the Elwro 800 Junior board.
The source files can be compiled with galasm like e.g.:
$ galasm io.pld
Target GAL16V8 can be programmed with a .jed file using TL866A or similar programmer.