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From: daveh@cbmvax.cbm.UUCP (Dave Haynie)
Newsgroups: net.micro.amiga
Subject: Re: Gotcha in MC68010 upgrade
Message-ID: <449@cbmvax.cbmvax.cbm.UUCP>
Date: Wed, 25-Jun-86 10:50:49 EDT
Article-I.D.: cbmvax.449
Posted: Wed Jun 25 10:50:49 1986
Date-Received: Sat, 28-Jun-86 05:18:39 EDT
References: <902@jade.BERKELEY.EDU>
Organization: Commodore Technology, West Chester, PA
Lines: 47

> 
> 
> I just made the MC68010 upgrade, following Thad Floryan's instructions
> to be found on Fish disk #18. There was only one problem, of the "I
> should have know better" sort. Since it can bite even the most
> experienced hardware tech (which doesn't describe me) as well as the
> hardware naive (which is closer to what I am), I thought I'd describe
> it to the net, in the hopes that others would avoid it.
> 
> If you understand which directions chips go on a board, you can skip
> this paragraph. If not, then dig out a chip - any chip. At one end
> should be a notch in the chip. This marks the end where pin 1 is. When
> replacing a chip, you should note which end the notch is on, and put
> the replacement in with the same orientation. Almost universally, all
> chips on a board have the same orientation.
> 
> On the Amiga motherboard, the 68K CPU is upside down compared to the
> rest of the chips. I made the blunder of pulling the chip before
> checking, then putting the 68010 in upside down (after all, that's the
> orientation everything else on the board had....). Reinserted the
> 68000 the same way, and got rather upset when it didn't work. After
> some gnashing of teeth, I decided to see if someone had been scumbag
> enough to put the 68K on the board upside down. Sure enough, it works.
> I'm typing this on a 68010-based Amiga.
> 
> 	Happy hacking,
> 	<mike

It nice when you CAN put all of the chips in the same direction, but its not
really that feasable on some of today's PC boards, like the Amiga.  The Amiga
PCB tries to squeeze in quite a bit on to a 2-layer board, while still having
have enough ground plane to pass FCC as a consumer product.  Reversing the 
68000 I'm sure would have been a layout nightmare even on a 4 layer board.
We did the same thing in the C128; several chips are reversed from the
direction you'd expect, mainly for layout simplicity.  This causes no problem
in assembly as everything is inserted by machine.  And at least on the C128,
every chip's orientation is indicated by the PCB silkscreen, and by a notch
in the socket if its a socketed chip.

-- 
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Dave Haynie    {caip,ihnp4,allegra,seismo}!cbmvax!daveh

   A quote usually goes here, but its currently being rennovated.

	These opinions are my own, though for a small fee they be yours too.
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