Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: A Question, a problem and an offer.
Message-ID: <15726@cbmvax.commodore.com>
Date: 8 Nov 90 18:18:48 GMT
References: <5331@crash.cts.com>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 50

In article <5331@crash.cts.com> orb@pnet01.cts.com (Randolph Turner) writes:

>  First the question:  It is to my understanding that the buss expansion port
>on an A1000 is virtually identical to that of the A500 with the exception of a
>7mhz clock line, and it's being upside-down.  

Not quite.  First, that's expansion BUS -- "buss" is an archaic synonym to 
"kiss", "Buss" is a fuse company.  But on to the question at hand.  The A1000
and A500 expansion ports are logically identical, and not flipped over.  If
you swing your A500 around backwards, so that the expansion port now faces
to the right, it'll be the same pinout as the A1000's, only an inch or so 
closer to your desk.  Don't try hooking things up to your A1000 or A500 
upside down; you may destroy both the device and the computer.  At best, it's
not going to work.

There is no 7MHz clock line on either port, though I think they made it easy
on some later A500s to jumper 7MHz out to the port or some-such, which would
make it easier to hook up A2630 type things.  But the ports, as defined, have
C1*, C3*, and CDAC clocks, but no C7M.  There is some slight difference in
timing of these clocks; basically, the A1000 had C1* and C3* locked very 
tightly to CDAC, which made it possible to create a C7M equivalent with C1*
XNOR C3*.  On the A500 with the old Fat Agnus, this 7MHz equivalent won't be
accurate enough, when combined with CDAC, to build a stable 14MHz clock, which
is what these Coprocessor boards use.

>  Now the problem (mine):  It seems that I have some sort of problem with my
>parallel port.  While it has absolutely no qualms about communicating with my
>printer, it fails to operate correctly (read that - at all) with either of the
>2, known working, homebuilt audio digitizers I have plugged into it.  If
>anyone has any idea what might be the problem, I would appreciate a response.

Sounds like those home-built digitizers may have some tolerance problems.  
What do they work with well enough to be pronounced "known working".  If it's
an A1000, you should realize that an A1000 can provide all kinds of +5V
current at the parallel port, while the A500 will give you about 10mA.  So
there's an awfully good chance these home-built digitizers aren't getting 
enough juice from the parallel port and should have have their own power
supply.  The only other obvious difference is pullup values on one or two
of the port lines -- the 8520 in the A1000 had internal pullups, the A500 
and A2000 version of the 8520 had beefed up output drivers which required
external pullup resistors.  This shouldn't be a noticable difference to most
things you hook up there, but beware, especially if your "thing" is home
made.

>Randolph Turner

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	Standing on the shoulders of giants leaves me cold	-REM