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May 20, 2020

Memoir 3 - UV PROM in a plywood box

My LSI-11 needed a console, attached over a current loop. I found a small Polish terminal that was suitable. Unfortunately, it was set to display KOI-7 encoding, and UNIX needed ASCII with lowercase letters. So, I set to re-program it. I opened the case, and the first surprise was that the case was made out of plywood. It was polished and painted from the outside, so I never suspected anything!

The firmware and the fonts were stored in a UV PROM. It was the kind of ROM that you needed to erase with ultraviolet light. Some people even erased them with direct sunlight. Through my connections, I found someone who had a programmer for it on the other side of town. Then, I read the ROM, found where the fonts were, and copied them. Then, I designed lowercase letters. I mapped them in a text file with asterisks, and then read that file with a simple program in C. The complete font is preserved in this picture (in an X bitmap, actually):

Once I packed the font back into the firmware, I went to the gentleman with the programmer and wrote it into the chip. The operation was a success, although ultimately led to nothing, even though the font had a last hurray later.

Next: Memoir 4.

Posted by: Pete Zaitcev at 11:25 AM | No Comments | Add Comment
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