Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!mailrus!ncar!boulder!tramp!hunt
From: hunt@boulder.Colorado.EDU (Lee Cameron Hunt)
Newsgroups: comp.sys.amiga.hardware
Subject: Confused about J300 on Amiga 2000 (rev 6)
Keywords: J300, Amiga manual
Message-ID: <24885@boulder.Colorado.EDU>
Date: 17 Aug 90 21:03:19 GMT
Sender: news@boulder.Colorado.EDU
Reply-To: hunt@tramp.Colorado.EDU (Lee Cameron Hunt)
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Organization: University of Colorado, Boulder
Lines: 42


When I was trying to get more slack from my floppy-drive cable in my
A2000, I accidently pulled out the jumper block on J300.  I didn't know
what position it should be in (either bridging pins 1 and 2, or 2 and 3) so
I consulted my trusty A2000 manual.

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.

Not having an A500, I opted to set it to the "normal" setting.  But before
I reassembled everything (I had to remove the power supply) I faintly
remembered a page on the specific functions of the jumpers.  I found the
page and read the description for J300.  The diagram with J300 suggested
that the "normal" setting was between pins 1 and 2, while the schematics
said that it was between pins 2 and 3.

I was, consequently, confused.

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?

So, I ask for help.  Email would be nice, but I'll also check this newsgroup.

p.s:  (to Dave Haynie and the hardware bunch) Jumpers, overall, are
a pain.  I realize that they are, in general, cheaper to use that software
registers; but I sure like the functionality of software-selected hardware
features such as the NTSC to PAL selectability on the "fat Agnus" and the
ability to switch from 68000 to 68020/30 on the accelerator boards.  IBM
had a good idea (parish the thought) by requiring no jumpers on their
microchannel cards.  Is Amiga considering doing similar things?  How
many jumpers are in the A3000?  (I hope few).


Thanks much,
--Lee
"Nothing is more disorginized than Calvinball!" -- Calvin & Hobbes
hunt@spot.colorado.edu   ...!ncar!boulder!spot!hunt