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From: grr@cbmvax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Cable to hook up Philips multi-sync monitor with amiga 500
Message-ID: <2432@cbmvax.UUCP>
Date: Tue, 29-Sep-87 17:58:00 EDT
Article-I.D.: cbmvax.2432
Posted: Tue Sep 29 17:58:00 1987
Date-Received: Fri, 2-Oct-87 00:42:35 EDT
References: <164@geocub.UUCP>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 58

In article <164@geocub.UUCP> anthes@geocub.UUCP (Franklin Anthes) writes:
> 
>  I've hooked up a philips multi-sync monitor (CM 8873) to my amiga 500.
> 
> I got the description for the cable to make out of a german computer mag
> called 68000'er. The cable they said to make went like this :
> 
> 	CM8873		AMIGA
> 	  1      GND	13,16
> 	  3	 RED	3
> 	  4	 GREEN  4
> 	  5	 BLUE	5
> 	  7	 CYSYNC 10
> 	  8	 HSYNC  11
> 	  9	 VSYNC	12
> 
>   All fine and well, the only problem was that this didn't work!
> 
> I tried disconnecting the HSYNC and VSYNC signals, and then the connection
> worked!
> 
> Just for fun I tried reconnecting HSYNC and VSYNC, while disconnecting
> CSYNC. The result of this experiment was that the machine wouldn't boot
> anymore!  The power light came on and that was it.  But if I connected the 
> monitor once the amiga had booted everything seemed to work fine.
> I tried this out friends amiga 1000, and it booted fine.
> 
>  Now could someone tell me :
> 
> 	a: what video sync signals should I have hooked up to get the most
> 	  out of my monitor?
> 
> 		1: CSYNC
> 		2: HSYNC+VSYNC
> 		3: both of the above
> 
> 	b: Why doesn't my amiga 500 boot when the HSYNC and VSYNC signals are
> 	  present, while my friends 1000 does fine with the same signals?
> 	  And of course what can I do about it?

The HSYNC and VSYNC pins are acutally input/output pins that can be used
as sync/reset inputs in genloc mode.  As a result they are not externally
buffered, and are not really intended for driving heavy loads or cables.

If your monitor supports CSYNC, then this is the best choice.  If it only
supports separate syncs, but doesn't work with the Amiga, the first thing
to try is putting a resistor in series with the HSYNC and VSYNC pins.
Values from 100 - 470 ohms have been known to work nicely.  If this doesn't
work, you need to build a little buffer circuit.

The A500 uses the vertical sync signal for the internal clock while the
A1000 uses a line-frequency signal from the power supply.  In either case
the computer will not boot if the clock signal is screwed up.

-- 
George Robbins - now working for,	uucp: {ihnp4|rutgers|allegra}!cbmvax!grr
but no way officially representing	arpa: out to lunch...
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)