ROM SIMM Pinouts

[Dennis Nedry]

I derived a pinout for the old Mac IIfx/IIsi/IIci ROM SIMM from some info found at Gamba's place together with a specsheet for the Atmel chips he used on his custom SIMM. I was unable to find any ROM SIMM pinouts online, though, and I know I've seen them. Does anyone have any pointers so I can double-check my work? I'm also interested in pinouts for any other ROM SIMMs for other Mac models.

 

[Trash80toHP_Mini]

Does anyone have any pointers so I can double-check my work? I'm also interested in pinouts for any other ROM SIMMs for other Mac models.

Check the DevNotes, if they don't give you the ROM pinouts outright, you can pretty much determine which address/data lines were left unimplemented from the full memory bus from the info in the memory map diagrams and the Block diagrams. IIRC, it's just a subset of the Full RAM bus . . . say 24 bit for a 32 bit system.

I'll take a peek at "Designing Cards & Drivers for the Macinto . . ./whatever" to see if the pinouts are listed for the ROM Slots.

 

[Trash80toHP_Mini]

Dunno if you found the pinouts in the DevNotes or not, but Bound/Wood Pulp Based/Storage Media Rock!!!!!!!!! [] ]'>

i found out something very interesting about the Portable's ROM simm Pinout/Setup that's worthy of a thread all its own!

maybe it won't take me as long to get that info posted . . .

. . . or not . . . :

 

[Dennis Nedry]

VERY VERY interesting. I like the 2 address bits that are used only on the IIcx/IIci, that's fascinating. Interestingly, Pins 4 and 5 (A0 & A1) correspond with the A0 and A1 of the onboard ROM of my IIci, so i'm not exactly sure what this means. Also the alternate chip select (Pin 63) is interesting.

From what I can tell on my IIci:

ROM SIMM Pin 63 = +5V (not selectable)

ROM SIMM Pin 2 = Pin 21 on 68030 & Pin 25 on NuBus controller, C7 in Cache slot

ROM SIMM Pin 3 = Pin 22 on 68030 & Pin 20 on NuBus controller, B7 in Cache slot

 

[Trash80toHP_Mini]

VERY VERY interesting. I like the 2 address bits that are used only on the IIcx/IIci, that's fascinating. Interestingly, Pins 4 and 5 (A0 & A1) correspond with the A0 and A1 of the onboard ROM of my IIci, so i'm not exactly sure what this means. Also the alternate chip select (Pin 63) is interesting.

Methinks the alternate chip select will likely nullify the on-board ROM. Interestingly enough, the Portable's ROM SIMM can be used ALONG WITH the on-board ROM or it can replace the on-board ROM.

The ROM SIMM Slot on the Portable, IIRC, can address 4 MB of ROM and there are instructions/hints about designing and utilizing said ROM overage in GttMFH: Second Edition.

Just imagine the possibilities: the entire operating system and a small (?) boatload of data could be burned into modern ROM ICs with faster operating speeds than the RAM ICs of the Portable's vintage!

=8-b. . . . . . .

 

[LCGuy]

Just imagine the possibilities: the entire operating system and a small (?) boatload of data could be burned into modern ROM ICs with faster operating speeds than the RAM ICs of the Portable's vintage!

Ooh, good point! That would be very cool. I wonder though just how difficult it would be to make the machine check for a ROM disk at startup...you'd have to know a fair bit on how to program Mac ROMs....unless you were to somehow reverse engineer the code that the Classic uses to boot off its secret ROM disk, and figure out how to get it to work on a different model?

 

[Bunsen]

I wonder though just how difficult it would be to make the machine check for a ROM disk at startup...

There was some info on that in the John Bass MacSCSI thread, but IIRC it only applied to the original Mac 128.

 

[tt]

I derived a pinout for the old Mac IIfx/IIsi/IIci ROM SIMM from some info found at Gamba's place together with a specsheet for the Atmel chips he used on his custom SIMM.

Are you trying to fabricate replica SIMMs?

 

[Dennis Nedry]

I derived a pinout for the old Mac IIfx/IIsi/IIci ROM SIMM from some info found at Gamba's place together with a specsheet for the Atmel chips he used on his custom SIMM.

Are you trying to fabricate replica SIMMs?

I was thinking about it but time and resources currently do not allow for that. A socketed ROM SIMM would be cool because you could use it for all sorts of cool ROM hacking projects. Just pull the ROMs out, reprogram, stick them back in. Currently there's no easy way to modify ROM in any Mac that I'm aware of.

I'm thinking it would be interesting to hear a Mac IIfx belt out the first generation Power Mac startup sound when first powered on. Although this would be much easier on a Mac that already has a sampled audio recording for the startup sound.