Waitstate

The 28C256 EEPROM, which holds the BIOS, has been our go-to choice since the early breadboard days. Before that, we relied on EPROMs, which required UV erasure before every upgrade—a time-consuming and inconvenient process. Switching to an EEPROM significantly improved our workflow, reducing turnaround time. However, the 28C256 has a couple of drawbacks: It cannot be written in-circuit since it requires a 12V programming voltage, which the Steckschwein does not provide.

… on the way back to munich, we had some time to do a little code review of our gfx library. thinking about the cpu to video chip timings and again read the well known datasheets of the V9938/V9958. suddenly i got an enlightenment and we came to the following conclusion. as described in the datasheet (V9958-Technical-manual_v1.0.pdf) of the V9958 there are different timings given for different kind of writes. so as far as we understand there are the following timings