Adapting digital RGBI monitor to accept analog RGB

tony duell ard at
Wed Jun 15 08:13:58 CDT 2016

> Is the 15kHz RGB signal fundamentally the same as the VGA signal, except
> at a lower horizontal frequency? If not, how do they differ?

Basically, yes. 3 separate analogue video signals, one for each primary

The drifference might be the sync signals. VGA has two, basically think
of them as one to start a new scan line (horizontal sync), the other
to start a new field (vertical sync). Often analogue RGB as a combined
(or composite) sync, which is normally the logical XOR of the 2 
separate sync signals. Since they are of very different frequencies, they
can be separated again in the monitor.

There is also 'sync on green'. In this one the sync signals are combined
with the green video signal to make something similar to a monchrome
composite video signal. With separate red and blue signals.


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