Fixed 7.11A ROM to work with the Re-UD-80

A project log for Re-UD-80 - a larger display for Epson PX-4 / PX-8

The vintage Epson PX-4 and PX-8 computers have small LCD screens, with low contrast. This device fixes that problem.

fjkraanfjkraan 03/02/2024 at 07:460 Comments

As previously reported, the 7.11A ROM didn't work properly with the Re-UD-80 because of the video sync signal configuration. The 5.21E ROM used one pin for both horizontal and vertical sync, the 7.11A ROM used two pins. The board can be modified to work with the 7.11A ROM, but not without loosing5.21E compatibility. Adding a jumper would mean a new board version. Instead I attempted to change the configuration of the EF9345 video controller in the 7.11 ROM to match that of the 5.21E ROM. This was successful, resulting in the 7.11c ROM. The ROM image can be found in the Files section:

In total four bytes are different between the 7.11A and 7.11c version; the TGS configuration byte, one character of the permanent banner and the two checksum bytes.

With this result, I think the project is completed. It might be interesting to explore the features of the UD-80, but that has to compete with other planned projects.