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| Macintosh IIcx custom ROM |
Posted by: luRaichu on 2026-05-20 10:41:28
Hi,
I'm looking for a IIcx compatible ROM that only has the memory test disabled and is 32-bit clean. The examples I've found include a ROM disk which I don't want or care for. Thanks |
Posted by: frontein1 on 2026-05-21 21:29:44
My IIcx is down for the count right now. But you can drop a IIsi ROM in the IIcx. This would give you a 32-bit clean ROM.
So really you probably want a IIsi ROM with just the memory test disabled (and vicariously the ROM checksum altered to not fail) right? If so give the attached a run (assuming you have a SIMM and a programmer handy) |
Posted by: Bolle on 2026-05-22 02:08:33
This will do: https://68kmla.org/bb/threads/macintosh-se-30-rom-modifications.49789/
IIcx and SE/30 have identical ROMs.
Edit: a scratch that, I missed you were looking for 32-bit "clean" ROMs. |
Posted by: Joopmac on 2026-05-22 03:05:43
I know of and use this one http://synack.net/~bbraun/macsrc/iisi+romdrv0.9+nomem+nosum.bin
IIsi 32-bit clean; No ROM disk, and no RAM test
see http://synack.net/~bbraun/macromboot.html |
Posted by: luRaichu on 2026-05-22 06:59:20
So really you probably want a IIsi ROM with just the memory test disabled (and vicariously the ROM checksum altered to not fail) right? If so give the attached a run (assuming you have a SIMM and a programmer handy) Why is it double the size of a IIcx ROM? |
Posted by: croissantking on 2026-05-22 07:27:05
Why is it double the size of a IIcx ROM? The IIcx ROM was older generation, whereas the IIsi was a newer universal ROM, so it was expanded.
Apple doubled the size of the ROM several times between 1986 and 1998, eventually ending up with 4MB ROMs. |
Posted by: joevt on 2026-05-22 14:42:34
Apple doubled the size of the ROM several times between 1986 and 1998, eventually ending up with 4MB ROMs. 68K Macs stopped at 2 MiB.
The first 1MiB ROM is probably this one:
067c.15f1 1991-10 - 420DBFF3 - Quadra 700 & 900 & PowerBook 140 & 170
These are the 2MiB ROMs:
067c.30f1 1994-05 - B6909089 - PowerBook 520 520c 540 540c
067c.30f2 B57687A5 - PowerBook 550c
077d.10f3.1 1994-09 - 5BF10FD1 - Quadra 660av & 840av
077d.2bf1.6 1995-08 - 4D27039C - Powerbook 190 & 190cs
Power Macs switched to 4 MiB to add all the PowerPC stuff.
3 MiB for the 68K part (includes PowerPC stuff that runs in MacOS).
1 MiB for the PowerPC part (ExceptionTable/Startup, HWInit, Nanokernel, 68K emulator, and Open Firmware for PCI Macs). |
Posted by: luRaichu on 2026-07-11 09:51:47
How do I split the ROM into 4 parts? I made my own ROM SIMM and am programming each chip manually |
Posted by: Phipli on 2026-07-11 09:57:14
How do I split the ROM into 4 parts? I made my own ROM SIMM and am programming each chip manually Either write a little Python program, or the program that comes with TL866 devices has a slice and dice option in the save window I think
If you're struggling, AI will walk you through it 🙂 |
Posted by: luRaichu on 2026-07-11 10:30:19
AI will walk you through it 🙂 Thanks for slopping by
I found these commands here
srec_cat rom.bin -binary -split 4 0 -o U4.bin -binary
srec_cat rom.bin -binary -split 4 1 -o U3.bin -binary
srec_cat rom.bin -binary -split 4 2 -o U2.bin -binary
srec_cat rom.bin -binary -split 4 3 -o U1.bin -binary |
Posted by: Phipli on 2026-07-11 10:37:48
Thanks for slopping by
I found these commands here
srec_cat rom.bin -binary -split 4 0 -o U4.bin -binary
srec_cat rom.bin -binary -split 4 1 -o U3.bin -binary
srec_cat rom.bin -binary -split 4 2 -o U2.bin -binary
srec_cat rom.bin -binary -split 4 3 -o U1.bin -binary You... Do understand that there isn't a whole lot of difference between using a search engine to get someone else's solution... And using AI to explain how you do it?
Your irrational fear of software is really going to cause you issues through your life. "Sorry boss, I can't do my job because I refuse to use software that starts with the letter 'R', or that has green in the toolbar." |
Posted by: finkmac on 2026-07-11 17:38:25
look man, “ask AI” is a profoundly silly way to respond to luraichu’s question. |
Posted by: Phipli on 2026-07-12 00:21:50
look man, “ask AI” is a profoundly silly way to respond to luraichu’s question. AI is particularly good, while poor at more nebulous questions, at responding to this type of "how do I" where the answer is a single, or few commands that take a little bit of structured thoughts to get right and are in a modern language / OS. It is actually a perfect example to see how it can be useful. I really actually hoped they would, so that they would learn that not everything in life is black and white, and sometimes things don't have to be perfect to be useful.
To be honest - I was surprised they were asking for help as it is only a little logic puzzle, but does take a few minutes of thought to get what goes where right.
It isn't an odd way to respond, as it is the fastest way to the answer and more likely to be correct than an answer from someone on the forum.
I have literally done what he was asking for in the past (without AI!) but to respond I'd either need to spend some time double checking how his board is wired, having a good old think about what bytes go where from the words, or 15 minutes digging through old folders looking for what I wrote before, on top of that, I'm also fallible - as are other people.
Think about the answer he got in the end - he just googled it. What kind of better response would you expect to have got from a hand crafted flesh computer response?
Also, I pointed him at some software with the functionality built in. But you both ignored that. |
Posted by: luRaichu on 2026-07-12 20:04:54
So really you probably want a IIsi ROM with just the memory test disabled (and vicariously the ROM checksum altered to not fail) right? If so give the attached a run (assuming you have a SIMM and a programmer handy) I'm running this ROM now, but I don't see an improvement in boot time. On both ROMs it takes about 30 seconds from pushing the power button to the happy Mac icon appearing. While I'm here, I'd also like to try changing the startup sound |
Posted by: Phipli on 2026-07-12 23:33:15
I'm running this ROM now, but I don't see an improvement in boot time. On both ROMs it takes about 30 seconds from pushing the power button to the happy Mac icon appearing. While I'm here, I'd also like to try changing the startup sound Since you had the machine apart, did you have the disk selected as the boot device in PRAM? If the battery has been out and the disk isn't selected, it will take its time scanning the SCSI bus. |
Posted by: frontein1 on 2026-07-13 09:31:42
Also how much RAM do you have installed? If not much, skipping the memory test probably won't save much time anyway. |
Posted by: luRaichu on 2026-07-13 10:00:21
Also how much RAM do you have installed? 65 megs |
Posted by: croissantking on 2026-07-13 10:13:15
65 megs is enough that skipping the memory test would be helpful. |
Posted by: frontein1 on 2026-07-13 10:40:41
IIcx compatible ROM
65 megs is enough that skipping the memory test would be helpful.
Haven't dug into this one yet. But the IIcx has a different memory controller than the IIsi. So if we are using a IIsi ROM that is not patched at the correct offsets for the IIcx.... Then when inserted in the IIcx, the machine could still be doing the memory test. Just a hypothesis right now.
EDIT: Scratch that, maybe this isn't an issue. Yes different memory controllers, but they both end up calling MOD3TEST and REVMOD3TEST. So after thinking about this, this hypothesis is likely flawed. |
Posted by: frontein1 on 2026-07-13 11:04:11
Probably a small consideration, but there should be a ROM select jumper on the board. Did you remove that jumper when you installed the ROM SIMM? |
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