17 May
2016
17 May
'16
1:56 p.m.
1. Some sites talk about e.g. arcade graphics as being "analog CGA" -- I
was acquainted with these being called "analog RGB" but never saw
"analog"
and "CGA" together before.
I susepct it means that it's 3 analogue signals (one for each colour) at the
CGA (== US TV, RS170) scan rates. As opposed, say, to VGA which is 3
analogue signals with a rather higher horizontal scan rate.
2. There are computers knocking about with actual
digital RGB signals, like
the BBC Micro B (IIRC). What I forgot to make explicit in my question was
Yes, it dodes. The BBC micro has 3 TTL signals on the RGB connector. A
total of 8 possible colours.
that I was asking about RGBI (+intensity), which AIUI
is the same as CGA.
Normally yes. I don't see any reason why RGBI signals could not be used
at a different scan rate, but AFAIK no machine ever did.
Now, I'm confused about point 1: did actual PCs
with CGA have both digital
(TTL) and analog signaling?
Not really. The original CGA card, and most clones, have a composite video
output too with NTSC-encoded colour, but that is not what you are asking
about.
-tony