Some days ago, using the latest discoveries in the schematics, I dedicated some time to understand the content of the glue logic ROM 28L22.
It is used to drive the blink, underline, and show video circuits to create mixed effects.
Actually: the underline hardware circuit should be renamed simply to line circuit, because it is the ROM that decides wether it is an underline, an overline, or both.
The ROM also mangles the row address lines in certain situations, to allow their repetition, and the creation of the "vertical stretch" effect.
TODO: I am not sure about the 0-6,7-13 vertical stretch division, it looks like this in the ROM, but maybe I accidentally missed a row, because adding this exception produces (an obvious) blank line which splits the gliph. I'll check again as soon as I can.
Some days ago, using the latest discoveries in the schematics, I dedicated some time to understand the content of the glue logic ROM 28L22.
It is used to drive the blink, underline, and show video circuits to create mixed effects. Actually: the underline hardware circuit should be renamed simply to line circuit, because it is the ROM that decides wether it is an underline, an overline, or both.
The ROM also mangles the row address lines in certain situations, to allow their repetition, and the creation of the "vertical stretch" effect.
TODO: I am not sure about the 0-6,7-13 vertical stretch division, it looks like this in the ROM, but maybe I accidentally missed a row, because adding this exception produces (an obvious) blank line which splits the gliph. I'll check again as soon as I can.