Date: Sun, 1 Aug 2004 17:46:45 -0700 (PDT) From: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
I have had diffiuclty finding a IIsi or IIfx rom sim to place in my SE/30. I have a IIsi, but the rom bank is blank, so it must be soldered on the motherboard somewhere. (Why is there is an empty rom slot?) In the past, I have used a program to "copy" the rom of a Macplus to use in a game simulator on a PowerMac (i.e., Macmame). Would it be possible to use this program to copy the rom from a IIsi and use it in an SE/30? Could that soft "rom" be copied onto a blank rom?
Gamba (who seems to have vanished, though his website is still up, thank goodness) and I did in fact build a ROM SIMM, copying the contents of the IICI ROM to blank chips and installing them on a ROM module circuit board. This successfully worked in an SE/30. The same could be done with a IISI or IIFX
It was a fun experiment, however, we ran into one significant (for us) obstacle. The ROM SIMM circuit board is ~.050" thick. The standard thickness on today's circuit boards is .063". So it's almost impossible to find .050" circuit board. In our case, Gamba filed the board down to the proper thickness by hand, which was difficult, time consuming and not anything that he wants to repeat (nor that I would like to attempt).
Significant obstacles for other folks would be extracting the ROM code and getting it programmed into chips properly. In our case, I desoldered the ROM chips from a IICI board, read their contents on a chip programmer (a specialized piece of hardware) and then programmed blank flash memory chips with the contents. I also determined which data pins on the chips would connect to which pins of a ROM module. Then I sent the chips to Gamba, and he designed, etched and fabricated the ROM module board (printed circuit board), soldered down the chips and tested the assembly in a IICI (using the ROM slot) and in an SE/30.
We also used a program to copy the ROM code directly to floppy (as the poster suggests above), which I then compared to what we extracted directly from the ROM chips. At first, it appeared that there were differences, putting us in doubt of the usability of the ROM extracting program. However, a later check seemed to indicate that the two methods yielded the same code, so perhaps I made a mistake on the first comparison. I'm still a little dubious about the ROM extraction program, though, in theory, it should work fine.
Finally, the ROM code is interleaved across four ROM chips. So the first byte of the ROM code is stored on the first chip, the second byte on the second byte, etc. then the fifth byte is stored on the first chip, the sixth on the second chip, etc.
If you extract the ROM contents using software, then you need some way to spread every fourth byte across chips. Many of the chip programmers have this ability included in their software, but it could be an issue.
The primary thing, though, is that you need access to a chip programmer, to get the code onto blank chips, and you need the ability to build a circuit board that will plug into the ROM SIMM socket, hold the programmed memory chips, and connect everything up properly.
Jeff Walther
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