BYTE: Part 4 (RGB video output)
28Sorry - long one again, but I've made progress!
Okay, so it turns out the RGBS video output pinout in the manual was all wrong.
It has a 7-pin DIN and my copy of the manual only lists five pins being used, whereas there is an errata that apparently came with a later-produced example that lists the additional two pins as being used. In addition, the original five pins are mapped wrong!
My original wiring was (as per the manual):
Pin 1 = video synch (Видео синхронизация)
Pin 2 = ground/common (Общий)
Pin 3 = green
Pin 4 = blue
Pin 5 = red
Pin 6 & 7 = not connected
The correct wiring seems to be:
Pin 1 = composite video (Видео) - not connected in mine
Pin 2 = synch (Синхро)
Pin 3 = blue
Pin 4 = green
Pin 5 = red
Pin 6 = ground/common (Общий)
Pin 7 = sound (Звук)
So only pin 5 (red) was correct! I had the synch connected to ground on the GBS8200, and there was no ground connected from the BYTE to the GBS8200 (as I only had a 5-pin DIN and pins 6 & 7 weren't listed as being used).
Anyway, fixing the wiring resulted in an image being displayed finally! The machine still doesn't appear to be working (flashing garbage on screen), but it does explain the data I was seeing when the logic analyser was connected to the D0-D7 pins of the UB880 CPU.
DRAM is a common point of failure in Western computers ... I suspect COMECON ones will be just as prone to failure so that will be my next avenue of investigation. Of course, the ROM may also have failed ... let's see.
My copy of the manual is here:
https://archive.org/details/byte-computer-moldova-1992/mode/2up
Thanks to Jose's posting the relevant snippet of the errata!
https://retroordenadoresorty.blogspot.com/2020/10/byte-computer-clone-de-la-urss-moldavia.html