Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: TICK and J300
Message-ID: <6873@cbmvax.UUCP>
Date: 15 May 89 16:19:38 GMT
References: <3319@hplabsz.HPL.HP.COM>
Distribution: na
Organization: Commodore Technology, West Chester, PA
Lines: 47

in article <3319@hplabsz.HPL.HP.COM>, dleigh@hplabsz.HPL.HP.COM (Darren Leigh) says:
> Summary: B2000 power supply fixed!

> I take it that this [TICK] has some sort of
> 60 Hz clock on it?  My 2000 didn't work until I changed jumper J300
> from "normal" to "A500".  What do I gain/lose by not having a power
> supply TICK?  Will it matter at all?

The TICK from the power supply gives you a 60Hz signal derived from the AS
line frequency, which is regulated by most power companies so that digital
clocks can be real accurate.  The CIA chip that drives the software clock
is based on this.  If you use the "A500" position, the timebase will
instead be based on the vertical sync frequency.  This is slightly off from
60Hz, I don't recall exactly how far, though the end result is that you're
clock won't be quite as accurate.  Genlocks will often cut the vertical sync
pulse every other frame, so unless you're using a genlock or you're in need 
of a real accurate TOD clock, you probably won't notice the change of the
jumper.

> Are the schematics for this jumper wrong?  For "normal" operation, the
> schematics say that J300 should be jumpered between pins 2 and 3.  I
> found it jumpered between 1 and 2 and had to change it the other way
> to get it to work without the TICK line.  What's going on?

Far as I know, the jumper's in right, though occasionally things do get 
swapped between schematic and actual layout.  From what you've said, the
jumper was in the right place as shipped, and you now have it in the A500
position.  

> P.S.  Mucho thanks to C-A for putting the 2000 schematics right in the
> back of the intro. manual which is included with every machine.  Also
> kudos for making the TICK line jumperable.  I hate having to cut and
> solder.

I figured that allowing the 2000 to use the A500 method of clocking would
help out if anyone ever wanted to power the 2000 from a DC supply, or if
someone ever found a legidimate use for having the TICK line synced to the
frame sync.  I guess you found another use...

> Darren Leigh   (415) 857-6713 (w), (415) 967-8102 (h)
> Internet:  dleigh@hplabs.hp.com
> UUCP:      hplabs!dleigh

-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
              Amiga -- It's not just a job, it's an obsession