Xref: utzoo comp.sys.amiga:61314 comp.sys.amiga.tech:13195 comp.sys.amiga.hardware:2433
Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!rutgers!cbmvax!grr
From: grr@cbmvax.commodore.com (George Robbins)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech,comp.sys.amiga.hardware
Subject: Re: A3000 Video Chips
Message-ID: <13076@cbmvax.commodore.com>
Date: 6 Jul 90 13:10:00 GMT
References: <4741@munnari.oz.au> <13060@cbmvax.commodore.com> <16713@windy.dsir.govt.nz>
Reply-To: grr@cbmvax (George Robbins)
Organization: Commodore, West Chester, PA
Lines: 28

In article <16713@windy.dsir.govt.nz> SRWMCLN@windy.dsir.govt.nz (Clive Nicolson) writes:
> In article <13060@cbmvax.commodore.com>, peter@cbmvax.commodore.com (Peter Cherna) writes:
> > The ECS chipset is capable of both NTSC and PAL.  In the A3000, there is
> > a jumper to select the mode of the machine.  On A2000's with ECS, I think
> > you have to cut a trace/add a wire to do the same thing.  So to summarize,
> > you do not have to replace your video chips to convert an NTSC 3000 to
> > PAL or vice-versa.
> 
> But does the jumper change the colour sub carrier frequency too, or just the
> number of lines. That is exactly what does the jumper change.

NO...

The "subcarrier frequency" or more properly the system clock frequency is
determined by the frequency of a crystal oscillator on the main board.  For
NTSC it's 16*Fsc, while for PAL it's 16*(Fsc*4/5).  For one reason or another,
these numbers are about 28 Mhz and within 1% of each other so it doesn't
make a whole lot of difference....*except* if you are trying to generate
composite video, where a 1% error in reference frequency is way out of the
ballpark.

The jumper changes 1 bit in the Agnus ID read register and determines the
initial state of the PAL/NTSC bit in the BEAMCON0 write register.  The rest
is up to the software.
-- 
George Robbins - now working for,     uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing:   domain: grr@cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)