Date: Thu, 31 Jul 2003 23:10:53 -0700 (PDT) From: Gregg Eshelman <[EMAIL PROTECTED]>
--- Jeff Walther <[EMAIL PROTECTED]> wrote:
According to "Designing Cards and Drivers for the Macintosh Family", 3rd Edition, Table 1-1 the ROM slot allows expansion to up to 64 MB of ROM. Anyone know if that's a misprint?
Well, again, unless there's misprinting present--it does say 64 megabytes. And all the other figures in the row on the table are in Xbytes, so I think they meant megabytes and not megabits.Yeah, 64MB (or did they mean megabits?) would be pretty nifty. Could place a complete install of Mac OS 7.6.1 in ROM. :)
According to this table the IIx, IIcx and IIci are all expandable to 64 MB of ROM. Interestingly, though, the table lists the IIsi ROM as being 512 KB in one ROM SIMM, when it was soldered down on most machines. Curious. This book includes info on the Q700 and Q900, so they should have had final info on the IIsi available.
The Q700 and Q900 are listed as having 1 MB of ROM expandable to 4 MB. The IIfx is listed as just having "512KB standard in one ROM SIMM"--no expansion capability listed. The SE/30 is not listed as this table only lists machines with NuBus slots--the IIsi is on there because there's a NuBus adapter for it.
Hmmm. I did a bit more browsing. This book (I just got it on Wednesday) is full of interesting stuff. It has the pinouts for the various PDS slots. The IIsi and SE/30 are identical--except--there are three reserved (unused) pins on the SE/30 which are used on the IIsi. The signal load capacities for the two machines also differ somewhat, but if you design for the lower of the two, that shouldn't be an issue.
Also, there's a description of the IIfx PDS slot, which has always been a bit mysterious to me. I've heard that it's not quite a PDS slot and difficult to build cards for, but I never understood why.
Apparently the IIfx has two main busses. One is the CPU/memory bus which runs at 40 MHz. The second is the I/O bus which runs at 20 MHz. Both of these are clocked by an 80 MHz oscillator, which is halved for hte CPU bus and quartered for the I/O bus. The problem with the IIfx PDS slot is that it lives on the slower I/O bus. So any card plugged in there only has 20 MHz access to the computer's systems. So, if you're installing a CPU upgrade card, it will have slower access to system RAM, and you must add some extra circuit gymnastics to make it work at all. It probably made building a separate upgrade for the IIfx a low volume proposition that just wasn't worth it.
One final tidbit I turned up is that the text claims that it should be trivially easy to adapt expansion cards for the SE to the SE/30.
Jeff Walther
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