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From: knudsen@ihwpt.UUCP (mike knudsen)
Newsgroups: net.micro.6809,net.micro.amiga
Subject: Re: RGB Monitor Compatibility
Message-ID: <1185@ihwpt.UUCP>
Date: Mon, 27-Oct-86 15:11:07 EST
Article-I.D.: ihwpt.1185
Posted: Mon Oct 27 15:11:07 1986
Date-Received: Tue, 28-Oct-86 02:24:05 EST
References: <475@vaxb.calgary.UUCP>
Organization: AT&T Bell Labs, Naperville, IL
Lines: 49
Xref: watmath net.micro.6809:998 net.micro.amiga:5601

> I currently own a (lowly) TRS80 CoCo running OS9.
I assume this apology is for net.amiga only! ;-)

> Like all sensible people, I really want n Amiga,
> but like many sensible people, can't afford one.
What's wrong with Atari ST?  Not that I should talk,
having just bought a Coco III (very sensible, non?)

> One possibility is to buy the new CoCo III that
> has just been released by Radio Shack.  The CoCo III
> uses an analog RGB monitor, just like the Amiga.
> Well, not quite, the CoCo has separate RGB and sync
> signals, whereas (if my info is correct) the Amiga
> tacks sync onto the G (green) line.  Is this true?
> Is there anyway to adapt the two?  This would allow
> me to buy a CoCo now, and later expand to the Amiga
> while not losing the greater part of my investment.

Good idea.  I can't speak for most monitors, but my
lowly (really -- lo-res TV dot-pitch) Zenith 131 that
I paid $150 for has both composite and analog (whew!) 
RGB inputs.  These have two pins each for either polarity
of separate H and V synch.  However, the manual says you
"must apply composite sync to both H and V."
I suspect you could just feed the Amiga Green signal
to both +sync pins.

I 'scoped my Coco III RGB outputs and found that both syncs
are positive TTL (full 5 V) pulses, whereas the video RGB
leads are much less.  The Amiga could certainly superimpose
5-volt pulses on top of the Green; the right monitor would ignore
the low-level video but trigger on the pulses.

Find out what the Amiga G & Sync looks like.  If it's as above,
then both computers should be able to share a monitor whose
sync thresholds are high enough.

Be sure to get a monitor with separate sync inputs and strap
the G to both of them.  That is, Radio Shack's monitor may
work with the Amiga, but not the reverse!

A friend is looking into your same question wrt the ST,
and I'm making up a cable to run the COco III into my Zenith.
Will keep you "posted" -- mike k
-- 
Mike J Knudsen    ...ihnp4!ihwpt!knudsen
Bell Labs (AT&T)   (312)-979-4132 (work)
Nobody pays for my opinions, which are mine alone.
"A mind is a terrible thing to waste, but the pay is good."