Well, I did it. I got ‘er working. Mostly! Thanks to the people on the Videobrain/Channel F list for their help. The problem that prevented it from working was dumb. There were two pins swapped to the UV201. Pins 35/37 on the schematic to be exact. I figured this out using an Excel spreadsheet of the chip connections that was done by Sean Riddle. I was comparing the schematic to the spreadsheet and found the problem. After swapping those two pins, things started looking much better. Almost fine in fact, on the logic analyzer. It was no longer hanging up and the video pins seemed to have some activity too. Soooo, I hooked the monitor up and was prodding the R-Y and B-Y and Y outputs from the video circuit, and got some recognizable text on the screen! Score! Looks like the ‘brain can do 16 colours maximum (unless there’s something I missed), since all video data must come out of pins 2, 3, 4, 5 on the UV201. Pins 19/20 on the UV202 appear to be composite synch and blanking it looks. So enough of that, how does it look?
WOOT! Look at that! I got the best looking Videobrain evar, in RGB no less. I know colours aren’t 100% correct, but we’ll get to that later. I need to translate the 16 colours it can do into RGB values then devise a circuit to produce this. One thing I found interesting is the Videobrain appears to output interlaced video. Fan-cee.
I played around with the text editor doodad and typed some random stuff. Interestingly, if you press shift, the screen goes all wonky in places, and stays that way until you press shift again! Only while shifted does it screw up- and interestingly it will screw up on every screen if the system is “shifted”. If you press shift again, video is fine. I am not sure if this is an ASIC issue, or a hardware one (i.e. the final version of the system was fixed up somehow to prevent this issue).
Here’s that screwy thing going on. You can see 5th through 7th rows are all wonky. The pixel data randomly “shifts” up and down. There’s no apparent pattern to the shifting.
Lol. Who’d want a clock or alarm on this thing? I can’t quite figure that out. Oh well, that seems to work in any event.
And finally the colour test. Yep it looks a bit hosed up. I am using 3 of the ASIC pins inverted to generate RGB into the monitor. This is just a hack so I can play around with it. So that’s it for now- I got it working (mostly) and I will be testing the games out soon. I have them all burned onto a single EPROM with some jumpers to select a game.