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Reverse Engineering the Macintosh IIsi Logic Board

Trash80toHP_Mini

NIGHT STALKER
That would be good, but I don't have contact info.

Scanning and distribution discussion would have its place in the lounge, not here in the open threads, Admins permitting.

Short Version: Intellectual Property Law is a sticky wicket. What was leaked onto the web from BOMARC (and others) was a travesty of in terms of betrayed trust. I don't plan on adding to harm already done in the near term. I'm old school, I bought all my software, paid my ShareWare licensing fees and only ever once copied a floppy because my business partner insisted. Not a great fan of the AbandonWare concept, but very appreciative of those working hard at conservation efforts.

/end of tangent
 

mmu_man

Well-known member
Well I'm even more old-school, I consider schematics ought to come with the hardware you buy, just like was common practice 40 years ago. :p
 

dougg3

Well-known member
Speaking of which, has anyone booted a IIci from the IIsi ROM? Does the IIci crash and burn when Audio In hardware test fails to pass muster at POST?
I have! The IIsi ROM works fine with all of the previous II series machines and the SE/30. (Well, I don't know if it's been tested on an original II...) In fact, the special patched ROM with the ROM disk driver and everything (originally done by bbraun, improvements made by BMOW now bundled on the ROM-inator II) is based on a IIsi ROM image.

There is code in the ROM that detects which machine it's running on and runs the correct routines that go with that machine. Not all new ROMs are backwards compatible, but some of them are.
 

Trash80toHP_Mini

NIGHT STALKER
Thanks for popping in, doug! Interesting about the ROM having the machine check its ID and then running tests based upon that.

If we eliminate Audio Input from the IIsi board, will it be necessary to fool ROMinator II into thinking its living in a IIci so it won't run the IIsi Audio Input hardware tests? Might failure to detect any such hardware on the board pass startup test?

The edges may wind up getting a little blurry between si and ci schematics.

Well I'm even more old-school, I consider schematics ought to come with the hardware you buy, just like was common practice 40 years ago.
Yep, I've still got the tube receiver with the schematic plastered to the inside of the case that I bought around about 1980. I think I may have the schematic inside an A/V receiver from about 2000. But that was electronics. This newfangled computer stuff has been hushy, hushy, secret stuff with high pressure magic smoke containment equipment on board so you're not supposed to mess with or even talk about it according to the manufacturers. 🤐
 

Trash80toHP_Mini

NIGHT STALKER
The IIsi ROM works fine with all of the previous II series machines and the SE/30. (Well, I don't know if it's been tested on an original II...) In fact, the special patched ROM with the ROM disk driver and everything (originally done by bbraun, improvements made by BMOW now bundled on the ROM-inator II) is based on a IIsi ROM image.
Reread the disjointed reply I made above, not there yet I think? Specifically: is the IIci ROM forward compatible with the IIsi? ISTR testing the IIci ROM in the IIsi for you and it failing to boot?

Lack of Audio Input kluge in a simplified IIsi board would be the problem here. If the full IIsi hardware test runs upon detection of the IIsi Machine ID have we got a roadblock for the standard ROMinator build?

If roadblocked:
1) how hard would it be to update the IIci ROM or hamstring the IIsi ROM to boot the unholy crossbreed?
2) how difficult might it be to conjure up a new Machine ID out of thin air for such a thing's hardware test?
3) might it be possible to display a new name for the mutt in About this Macintosh and TattleTech reports?

If we weren't all crazy . . . 🤪
 

Trash80toHP_Mini

NIGHT STALKER
I could use the help of a whiz-bang AI operator to do a bit of volunteer work for this project. My OS9 Graphic Arts production system is down until I can get the QS'02 back online or finally get the MDD/FW400 special edition backup machine up and running. I'd like to clean up the centerfold of the IIsi schematic for this project. An editable PDF file as exported from AI9 for markup in AI9 running under OS9 would be the point of the exercise. Dunno, but I'm sure that would be easily done in rentware versions of AI if they can export AI9 files I can use when I get the lead out of my machine maintenance and setup knickers. PM if interested in helping out and we can get started there on teasing it out into system specific layers. THX :)
 
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Trash80toHP_Mini

NIGHT STALKER
Run-up thread to this one reactivated:
Thinking in terms of system speed and flexibility for combination NuBus/PDS riser design options. The crystal can quartet on the IIsi redux needs to stay in harmony.
 
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dougg3

Well-known member
Reread the disjointed reply I made above, not there yet I think? Specifically: is the IIci ROM forward compatible with the IIsi? ISTR testing the IIci ROM in the IIsi for you and it failing to boot?

I honestly have no idea, but I would guess that the IIci ROM would be unable to boot a IIsi. I haven't ever tested it because I don't have a IIsi. As for trying to get a "IIsi missing the audio hardware" to work: It's probably one of those things that you start by "just trying" with the original IIsi ROM and seeing what happens...
 

davidg5678

Well-known member
This is pretty cool! I'm a bit confused what the purpose of using a IIci rom in a IIsi would be, though. What advantages does the IIsi have over a IIci?

As best I can tell (at least from some preliminary Wikipedia-ing) , the IIci looks better than the IIsi in every way. Would basing this project off of the similar IIci architecture simplify some of the problems you are looking at? Is the IIci like a IIsi, but with less cost-cutting tradeoffs, or is that machine architecturally less useful?

I think it's an amazing concept to create a new logic board for the SE/30 using aspects of superior computer architectures from other contemporary Macintosh models. I wish you luck with the reverse engineering. (y)
 

Trash80toHP_Mini

NIGHT STALKER
Thanks, it's a lot of fun exploring the possibilities. The IIsi has always been considered to be in the MEH class of Macintosh, playing second fiddle to both the SE/30 and the IIci. But in many ways it's far superior to the SE/30, memory expansion supported not being one of them. :rolleyes:

If placed in the well of the SE/30, the IIsi architecture is a far more flexible platform in terms of expansion options than the IIci would be for running a vertical stack of cards and adapter slots up the SE/30 sidewall. ;)
 

Trash80toHP_Mini

NIGHT STALKER
. . . the IIci looks better than the IIsi in every way. Would basing this project off of the similar IIci architecture simplify some of the problems you are looking at? Is the IIci like a IIsi, but with less cost-cutting tradeoffs, or is that machine architecturally less useful?
Thanks for joggin' my noggin' with that last along with your question about the ROM issue. Was sleepy so it kinda blew by me while I was thinking about the comments @dougg3 made about the IIci ROM and my recollections of the wreckage when I tried the older IIci ROM in the IIsi.

Dropping the Audio In subsystem removes what's pretty much the only overall system level change between the two. Their components and I/O are arranged very differently, but they share the same RBV, MDU architecture so they're pretty much the same machine.

The only "cheapening" tricks were:
1) smaller, lower, unique form factor case
2) lower connector count
3) less slots required less power from the low. sleek design PSU
4) Combo ASIC developed for both the IIsi and LC condensed Serial Port and SCSI controllers.

Couldn't locate my SuperIIsi project box, but I'll take a pic later if & when . . . :rolleyes:

| NuBus Adapter/FPU | TwinSlot PDS Adapter | Isi Logic Board |

NuBus Slot $9/FPU -> top PDS Slot -> Bottom PDS = Improved/Rearranged IIci Application Specific Cache Slot -> IIsi Logic Board
NuBus Adapter in Top Slot is connected to Bottom Slot on TwinSlot adapter PCB used in blockish TXT diagram for "clarity" LOL!
IIci down two NuBus Slots and IIsi down Audio IN subsystem, but machine state = IIci ROM boot? = IIxi

@dougg3 cc @Bolle what does that machine state abomination look like to you? If Audio In subsystem disabled, I could test that exact configuration. Might not even need to go that far as the IIci ROM won't notice or test for Audio In function at boot? *IIci Machine ID Required however.

edit: for bonus points we could install an adapter/P33 combo in the bottom PDS slot! 🤪
 
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dougg3

Well-known member
My money is on there being other differences between the IIsi and IIci that lead it to being a more complicated change than just the audio in subsystem. I would place bets on the IIci ROM not booting a IIsi. But honestly, I don't think I can provide any value to this discussion other than to say "someone should try it" :cool:
 

Trash80toHP_Mini

NIGHT STALKER
I don't think I can provide any value to this discussion other than to say "someone should try it" :cool:
Maybe you can? Is there a hardware hack possible for setting Machine ID per the 475/605 jumper setup?

Does anyone out there know of something like iwishiwere(?) that might be able to set the IIsi PRAM up for IIci Machine ID on reboot? That one makes older machines think they're newer machines to run later System Levels, no? Never had a use for it, so an explanation or a link to one would be much appreciated right about here. :)
 

Trash80toHP_Mini

NIGHT STALKER
Last time I looked (some 12-20 years ago?) the Controller/Transceiver NuBus Chipset was still available from TI. Wondering if new/old stock parts from TI might be used to build DuoDock's Twin NuBus Slot implementation on an adapter for the IIsi board?

20MHz Docking Connector of Duo Series matches IIsi clock, but that 40MHz crystal can on there and the IIsi NuBus adapter makes me think it might work fine on the IIci 25MHz clock? NuChip 30-33 controller will probably work if the IIci/IIsi hybrid can be chipped that significantly?

IIRC, NuChip30 on IIci schematic would be the designation for 68030 upgrade of the Mac II NuChip ASIC. NuChip 30-33 notation seems max clock related?

NuBus subsystem works just fine on DuoDock with the ROM pulled, so it's independent of the rest of the mulifunction $E expansion card that is the DuoDock.

edit: STORM DSP and hot VidCard on NuBus SE/30 ladder would be amazing. /IRQ3 used by PDS NIC?
 
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