From: bull@vaxc.cc.monash.edu.au
Newsgroups: comp.sys.amiga.hardware
Subject: Re: 1200 with '040 ?
Date: 18 Nov 92 16:36:36 +1100
Organization: Computer Centre, Monash University, Australia

ajs@news.dcs.warwick.ac.uk (Andrew Satterthwaite) writes:

> OK, before anyone flames this for sounding daft, I don't know much about
> chip connections and hardware generally but I was wondering wether it would
> be possible to plug a 68040 into an A1200. I realise it may need a host board
> or something but surely it wouldn't be that difficult for GVP or someone
> to come up with something, and as it wouldn't need extra 32 bit memory (as
> the A1200 has got it already) it should be fairly cheap compared to A500/2000
> '040 accelerators.

        In theory it can be done, but in practice it may be a problem.
The A1200 has a 32 bit expansion trapdoor, similar to the A500's 16 bit
trapdoor (but the A1200 trapdoor is designed to be able to handle a
wider variety of devices than the A500 trapdoor). You could put an 040
on a board in the trapdoor, but the problem I see is heat. The 040
puts out more heat than even Motorolla thought it would when they were
designing it. If you look at the 040 cards made for A3000's, they have
either a heat sink or a small fan on top of the 040 to keep it cool.
Try putting an 040 in the A1200 trapdoor and you could have heat
problems.

        George Robbins, is there enough space in the expansion bay for
an 040 with a fan or heat sink? How good is the air circulation without
using a fan to force air through the expansion bay?

        The next point is 32 bit FAST ram. The A1200 has 2 megs of
32 bit CHIP ram (CHIP ram is the ram used by the graphics and sound
chips, Agnes, Paula, etc). When you're running graphics intensive
programs, the graphics chips get priority when accessing CHIP ram.
This means that if an 040 (or the 020 in the 1200) needs to use
CHIP ram at the same time as the custom chips, the custom chips
get first go and the CPU has to wait. If the only ram you have in the
A1200 is CHIP ram, this will happen a lot. The answer is to add
more ram, which will be recognised by the CPU, but not by the
custom chips (called FAST ram). The CPU can access FAST ram without
having to wait for the custom chips. Where do you add this extra
ram? On the trapdoor board? You've already got an 040 on that board
so putting extra stuff there is going to make the heat problem worse.
There are no sockets on the motherboard for FAST ram, so the other
alternative is to use the PCMIA slot, but it's 16 bits wide, not
32 bit.

        What about a piggyback setup like so many of the A500
accellerators use? The 020 is surface mounted (it's *soldered* to the
motherboard). You can't use a piggyback board because you don't have a
cpu socket to plug it into. Even if the 020 was socket mounted, you
would still have to deal with a case which may not be big enough to fit
an 040, and the heat problem crops up again.

>       Is this a daft idea, or is it a possibility ... If the latter what
> sort of price range would we be looking at (please quote in pounds sterling
> if possible as everyone seems to double the price of everything over here in
> England.

        I don't doubt that someone will try to develop an 040 board for
the A1200, but I have doubts over how reliable it will be. An 030 board
is more realistic since the 030 is smaller than an 040, produces less heat
and is cheaper.


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