vt278

[Tony Duell]

> >From looking at the prints, I can see where the video chip pumps out H
> sync, V sync, and video to the edge fingers... the board also needs
> +5, +12 and -12 (for the DRAMs, among other uses).  It's been years
> since I tore apart a VT100 (was turning two dead ones into one live
> one), but there's nothing magical about them... the video board
> schematic is in the VT278 drawings.  If you didn't want to muck around
> inside a real VT100, you'd need a mono video monitor that can handle
> the sync rates for 80 col and 132 col, whatever they happen to be
> (never poked at the video signals with an o-scope, so can't even
> hazard a guess).

Well, since the VT100 has a BNC connector on the back that outputs 
something close to RS-170 video, I'll guess that the horizontal sync rate 
is 15570Hz and the vertical 60Hz :-)

Combining the 2 syncs and the video to make a composite signal is a not a 
difficult problem. If necessary, start looking at the schematics of some 
1980's home computers to see how they did it (typically XOR the syncs to 
get a composite sync, then a couple of transsitors to combine that with 
the video).

-tony