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From: png@netcom.COM (Peter Glaskowsky)
Newsgroups: comp.sys.mac.hardware,comp.sys.m68k
Subject: Re: 68040 for 68030 substitution (question)
Message-ID: <1991Jun11.021641.6346@netcom.COM>
Date: 11 Jun 91 02:16:41 GMT
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 57

alanr@cecelia.media-lab.media.mit.edu (Alan Ruttenberg) writes:

> I was wondering if a 68040 can be substituted for a 68030 in a
> MacIIfx.  I understand that the pinouts and the clock rate (40Mhz 030
> vs. 25Mhz 040) are different.
>
> What I am curious about is what a minimal upgrade to a 040 would
> entail.  Can I buy a chip, and build a small adapter board? Or are
> there many changes that would have to be made.

Actually, the Motorola "MC68040 Designer's Handbook" (MC68040DH/AD),
a snazzy slip-cased 3-ring binder, contains a section entitled "MC68040
to MC68030 Bus Adapter Application".

There's a complete schematic with part numbers, and equation files for
all the PALs in the design. In short, it describes 100% of the necessary
hardware. There are some limitations; some of the bus interface
protocols are necessarily different, but these can be overcome with
the addition of some firmware and/or system software patches.

That's the rub... NONE of the necessary firmware/software is provided.

Paragraph 7.1.1, "Software":

"System software issues include differences in the memory management
structure, internal cache initialization and management, software
emulation of unimplemented floating-point instructions, emulation of
unsupported instructions, and the exclusion of the instruction
continuation exception model (i.e., bus error)."

The design requires the following chips:

MC88195 clock generator
6 PALs (3*22V10, 20R8, 16R8, 16R6)
9 TTL logic packages (74F139, 74AS20, 74AS32, 74AS00, 74F64, 74AS821,
                      74AS257, 2*74AS573)
8 bus buffers (74F543)

plus various passive components.

Now... maybe this is irresponsible speculation, but in the Mac Zone
ad in the July 1991 "MacWorld" magazine, there's a nice color picture
of a product called Magellan, from Total Systems. This is an
040 accelerator for the SE/30 or IIsi. (IIci and IIfx models are
promised but no prices are listed.)

It appears to me to have a special oscillator module, 7 PALs, 8
74FCT543's, and miscellaneous logic and passive components.

Could this be the Motorola circuit? Are they using some sort of INIT
to patch the system? I don't know. The product is reasonably priced,
but it's out of my range for the moment, and I have a IIcx anyway.

(Disclaimer: I'm not associated with Total Systems, Mac Zone, or
Motorola.)

.                       png