4M RAM expansion for the Portable ??

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Article #45686

#45686

From: Gary Kacmarcik
Date: Tue, 06 Feb 1990 10:45

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Has anyone had any success creating a 4M expansion card for the
Macintosh Portable??

We are currently working on developing memory upgrades for the
Portable and have succeeded with the 1M board, but the 4M (same board
BTW, just different SIMMs and a select resistor) will not operate as
4 Mbytes of memory.

If we turn off the decode for the high address lines, the 4M board
operates fine as a 1M board, but this is obviously unacceptable.

The Macintosh Portable Developer Notes(^1) mentions (many times, in fact)
that the RAM can be expanded using 1M and 4M expansion boards (Apple
has actually reserved 8M above the standard 1M for RAM expansion). To the
best of my knowledge, Apple has yet to introduce *their* 4M expansion
board. Is there possibly a problem with how the Portable accesses the
upper Megs of memory from the expansion card??

The diagnostics are:
	sad Macintosh w/
		D7.L = 0000 0003
		D6.L = 0000 FFFF

These codes are not really documented in the DevNotes, but one can
infer (from an example in the Notes) the there is a problem with RAM
Bank A.

Does anyone have any ideas as to what's going on here? Any comments
will be appreciated.

(Also, is there any way to boot beyond the "sad macintosh" when the
startup tests report a problem. It would be nice to be able to perform
a few diagnostics of our own to help track down the problem)

thanks in advance,


Gary J Kacmarcik
platypus@dsrgsun.ces.cwru.edu

(^1): Note that this document also states "Examples of the Macintosh
Portable customer are mobile business professionals (...) and
*STUDENTS*." Obviously Apple is unaware of the budget of the average
student :-)

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!usenet.ins.cwru.edu!alpha.ces.cwru.edu!platypus
From: platypus@alpha.ces.cwru.edu (Gary Kacmarcik)
Subject: 4M RAM expansion for the Portable ??
Message-ID: <1990Feb6.104558.8920@usenet.ins.cwru.edu>
Reply-To: platypus@alpha.ces.cwru.edu (Gary Kacmarcik)
Organization: CWRU Dept of Computer Engineering and Science
Date: Tue, 6 Feb 90 10:45:58 GMT