In the olden days, when 2732 EPROMs still were manufactured, flashing a new ROM for the Model I was easier. Since that is no longer an option, and there is no direct replacement for the TRS-80 ROMs anymore, people have been writing up methods to use a modern 27C256 EPROM.
Using a single 27256 EPROM
- To use install single 27256 EPROM in your 16K Model I follow these instructions written by Matt Boytim. You may need the referenced CPART file or the referenced FF2K.BIN file.
- The Dutch TRS-80 group also has a writeup on the same topic, found at https://trs80.nl/hardware/m1eprom/.
- Jürgen Büssert has also written up an article for both a 27256 and a 27128, which can be found at https://www.buessert.de/Technik/Museum/TRS-80/M1/ROM/english.htm. He has also developed a small PCB which will do most of the hard work. Unlike other solutions, the ROM does not need to be scrambled to use this solution. Anyone interested in the board should reach out to him by visiting his impressum page.
One point of note: You may need to verify that the motherboard does not have a solder bridge between Pin 7 and Pin 18 of ROM A. Some boards might have this. This bridge will prevent the EPROM from working.