This is my first post here. Hope one of you experienced programmers can help.
I am a member of a group of people that make and use S-100 bus based computers. See for example
www.S100Computers.com and www.n8vem-sbc.pbworks.com/w/page/4200908/FrontPage.
We design new boards and have done so now for video boards, RAM/ROM board and a number of CPUs (Z80, 6502, 8088, 8086, 80286, 80386, 68K etc). Amongst the ongoing projects is one to build a MSX compatible hardware platform. I have been working on the video/sound part of the project and while progress is slow we are getting there.
If you look at http://www.s100computers.com/My%20System%20Pages/VDP%20Video...
you will see I can get 40X25 chars/lines on the screen. However when I try to get 80X25 chars resolution I always end up with duplication of the top lines of text half way down the screen. It looks like I am not initializing some V9938 register correctly. The problem I have is I cannot find an example of code where the V9938 is initialized from reset to yield this resolution. I tried setting/resetting various bits in R#0 to R#9 etc with no luck.
Could somebody here provide Z80 source where from a “cold start” the V9938 in correctly initialized to display text in 80X25 format.


