Reverse-engineered Classic II

[Arbee]

Oh, here's the official Classic II schematic, in case I haven't posted it before.

 

[adespoton]

Thanks; I was going to say "couldn't you leverage debug pins?" but with the schematic, I can't see anything providing the ability to set an interrupt exactly there. That seems... odd. did they have them in the pre-production board and remove them for manufacturing?

 

[Andrewski007]

I must admit that I know very little about the hardware at at this point. I service commercial cooking equipment for a living. I was reading about the SuperIIsiHack and other stuff and wondered if the classic II had the ability to unlock potential now that modern power supplies and lcd screens are commonplace. Here's a link to the SuperIIsi thread-

https://68kmla.org/bb/index.php?threads/superiisihack%E2%84%A2-aka-se-30s-bane.24674/page-2

 

[btb]

Thanks for adding that @Arbee! If it was ever uploaded before, I sure couldn't find it.

It does seem a little crazy to leave out any slot IRQ line, but I guess they were just completely positive they never wanted to re-use the Eagle, like in a more capable machine.

 

[finkmac]

yeah this wasn't available before.. I think it was just the BOMARC version. very nice.

 

[Andrewski007]

Irq is the interrupt, right? Does it have to be in hardware?

 

[adespoton]

Irq is the interrupt, right? Does it have to be in hardware?

IRQ refers to the hardware interrupt handlers -- any processor will have a certain number of "slots" that can be used, with an associated value that can reference them on the software side. This is essentially the key way for a piece of hardware to pause CPU execution to do something, and then resume it.
Unfortunately, that means that it has to be in hardware. If it were in software, there'd be no way for the hardware to break the cycle to get the CPU's attention.

I haven't done commercial cooking equipment, but I've done commercial laundry and other devices that have processing hooked up to the hardware -- it all works the same way, generally with the IRQs linked to the physical controls and sensors; old style had actual analog switches that would draw the signal low to set the IRQ, more modern stuff usually has a secondary controller for the hardware interface that does much the same thing. Of course, really old equipment doesn't use a CPU at all and does it all in hardware -- but it still usually has a centrally controlled clock and circuit that needs similar abilities to interrupt flow at the hardware level for exceptions.

 

[Andrewski007]

Fryers are like you described, frymaster has multiple boards handling different tasks like automatic oil top off, filtering, temp/high limit control and ignition/heating element control. I see adb and scsi have irq pins, which makes a lot of sense now. Is it possible to steal a different interrupt to hack an input in? I'm thinking no, because it would look to address a different area.

 

[Arbee]

There is a specific place software looks for the slot interrupt status (and to clear it), called VIA 2. On a IIcx or SE/30 it's a real physical VIA chip. But on the Classic II that's buried inside Eagle for cost reduction, and the pins that would normally go to it seemingly have other uses.

 

[croissantking]

Oh, here's the official Classic II schematic, in case I haven't posted it before.

Thanks so much for this.
Is it redrawn? It’s a little different from the usual photocopied ones.

 

[Arbee]

As far as I know it's original. Some of them are just in blue for reasons I don't understand.