Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!cbmvax!rsbx
From: rsbx@cbmvax.commodore.com (Raymond S. Brand)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Confused about J300 on Amiga 2000 (rev 6)
Keywords: J300, Amiga manual
Message-ID: <13874@cbmvax.commodore.com>
Date: 18 Aug 90 00:06:44 GMT
References: <24885@boulder.Colorado.EDU>
Distribution: na
Organization: Commodore-Amiga Inc, West Chester, PA
Lines: 34

In article <24885@boulder.Colorado.EDU>, hunt@boulder.Colorado.EDU (Lee Cameron Hunt) writes:
> 
...
> 
> First I looked at the schematics and found J300.  It listed the pins (you
> must look carefully) 1 to 3 from right to left.  It also mentioned that
> one configuration was the "normal" setting while the other was the "A500"
> setting.
> 
...
> 
> I tried both postions on my power-on Amiga and I could find no difference.
> 
> The explanation about J300 was cryptic, but I think that I'd like the CIA
> to run off the 60Hz line clock rather than the monitor's sync clock.  But
> what does a lowly newly-graduated EE like me know?
> 
The jumper determines where the clock to the TOD counter on ciaA comes from.
There are 3 choices, 1) from the powersupply power-line tick, so that TOD
counter is as accurate as the power-line frequency; 2) from the monitor vert-
itcal blank signal, not recomended since it's frequency can be affected by
software (this is the "500 mode" since the 500 doesn't have a power-line
tick); 3) from nowwhere, not recomended.
> 
> --Lee

						rsbx

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  Raymond S. Brand			rsbx@cbmvax.commodore.com
  Commodore-Amiga Engineering		...!uunet!cbmvax!rsbx
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