platypus@alpha.ces.cwru.edu (Gary Kacmarcik) (02/06/90)
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 :-)