Going back to a thread a few weeks ago... I picked up an extra IIci motherboard (brand new, or at least unused and still sealed) for $3, because I didn't want to pull the ROMs from my IIci. So I guess I'll pull the ROMs from my old motherboard and use this new one.
Anyway, my plan was to pull the four DIP ROMs from the IIci, take them down to the local PC shop with an EEPROM programmer, extract the code, write the code to PLCC EEPROMs or Flash and then stick the PLCC chips onto the SE/30 ROM stick which I have. As I mentioned in that earlier thread, the SE/30 ROM has "512K ROM SIMM" silk screened on it. However the four chips installed are Atmel 27C512's (512Kbits) so that only adds up to 256K of capacity. In our discussion we more or less concluded that the ROM SIMM was probably built to go up to 512KB (with different chips) of capacity but Apple had only used half of the capacity in this case. Okay, simple. I find some 1 Mbit chips to program with the IIci code (IIci ROM chips are 1 Mbit, 128K X 8) and install them on the SE/30 ROM. This is the problem. The change from 512 Kbits to 1 Mbits of capacity also seems to invariably come with a change in the pinout of the EPROM chips. Obviously a previously N/C pin is going to become an address pin, but this is much more severe than that. Pin 22 switches from data to CE and pin 23 from CE to an address pin. Pins 24 and 25 make a similar switch with OE. Unless there was some very specific 1 Mbit chip which Apple had in mind, I think this blows our explanation for why this module is labeled 512K. Perhaps the label means that the chips used should be 512 Kbits each? There certainly doesn't seem to be any way to get 512 KB of storage capacity onto this module. Perhaps Apple designed this module before the 1 Mbit pinout was finalized and didn't know it would change that radically? This seems to make it much more difficult to adapt the IIci ROMs to the SE/30. Okay, next question (actually, I'm not sure there is a question in the above). Does anyone have the pinout for the IIsi ROM SIMM? I'm sure I could whip up some kind of adaptation or even run off a small board (when I have more money than I do now) but I'd need to know the pinout. I can figure most of the pinout from this SE/30 ROM SIMM, but there's going to be one more address line in the IIsi ROM SIMM (256KB vs. 512KB) which isn't apparent on this module. I'll need to know where that last address line is supposed to go. In other news... I saw this: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4610&item=2087361728 on Ebay. The interesting bit, to me, is that the adapter (about 3 cards back) for IIsi and SE/30 is identical to the one I picked up in the Goodwill Bins, *except* that the one I have only has the chip on the left side. This picture clearly shows a chip on the left and the right. My adapter has a place for a chip on the right but no chip installed. Anyone else have one of these in their SE/30? Does yours have one or two chips installed? I haven't actually got around to buying an SE/30 yet (maybe if I had the IIci ROM ready to test...) so I haven't tested my adapter to see if it works properly. As always, thanks for any helpful or humorous comments. Jeff Walther -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> The FAQ: <http://macfaq.org/> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
