20 ms·

It wasn’t mentioned. I think they are referring to how the Jonathan’s bus is more similar to S-100 than a PC’s motherboard card bus. There was not a primary mot

It wasn’t mentioned. I think they are referring to how the Jonathan’s bus is more similar to S-100 than a PC’s motherboard card bus. There was not a primary mother board that ran the bus like in Apple 2 or IBM PC I ran TSR-80 systems and I never had a S-100, I was always fascinated how it could have multiple motherboards on it with different CPUs. I think S-100 was more similar to SCSI or Ethernet than to a PCI bus.

convolvatron 3y ago
not really like scsi - that's more like usb with a central controller. more like VME - a bus that looked alot like a 68k bus, but supported multiple masters with a protocol to negotiate temporary ownership to assert a transaction. there was a single address space. so every board had a set of dip switches to give it its address. which was always a big source of pain I can't imagine apple shipping a computer product like that, so maybe you get the high bits based on what slot you're in and a config eprom to do discovery?
- flenserboy 3y ago
  I could see them using something like they did with NuBus — something similar to the declaration ROMs could make this sort of configuration work nicely, as long as part makers played according to the specs.
- leejoramo 3y ago
  Interesting. I suspect if Apple had done this they would have had someway for the cards to auto-negotiate. A few years after the Jonathan prototype, I remember fighting with the DIP switches on PC ISA cards and setting the the correct IRQs, and then seeing a friend drop in a NUBUS card into their Macintosh II and the hardware was magically configured. I wonder if NUBUS could have multiple masters?
  - rbanffy 3y ago
    Apple II cards knew which slot they were in and could have small ROMs with simple IO functions.
rbanffy 3y ago
IIRC, it's entirely possible to build an Apple II on an Apple II card and let it drive a completely passive backplane with slots 0 through 7. I think it'd even be possible to drive the bus from any slot. The Jonathan bus would probably be a lot more robust, however, as power delivery was an issue on loaded Apple II's (with too much current flowing through too few VCC and GND pins).

convolvatron 3y ago

not really like scsi - that's more like usb with a central controller. more like VME - a bus that looked alot like a 68k bus, but supported multiple masters with a protocol to negotiate temporary ownership to assert a transaction. there was a single address space. so every board had a set of dip switches to give it its address. which was always a big source of pain I can't imagine apple shipping a computer product like that, so maybe you get the high bits based on what slot you're in and a config eprom to do discovery?

flenserboy 3y ago
I could see them using something like they did with NuBus — something similar to the declaration ROMs could make this sort of configuration work nicely, as long as part makers played according to the specs.
leejoramo 3y ago
Interesting. I suspect if Apple had done this they would have had someway for the cards to auto-negotiate. A few years after the Jonathan prototype, I remember fighting with the DIP switches on PC ISA cards and setting the the correct IRQs, and then seeing a friend drop in a NUBUS card into their Macintosh II and the hardware was magically configured. I wonder if NUBUS could have multiple masters?
- rbanffy 3y ago
  Apple II cards knew which slot they were in and could have small ROMs with simple IO functions.

rbanffy 3y ago

IIRC, it's entirely possible to build an Apple II on an Apple II card and let it drive a completely passive backplane with slots 0 through 7. I think it'd even be possible to drive the bus from any slot. The Jonathan bus would probably be a lot more robust, however, as power delivery was an issue on loaded Apple II's (with too much current flowing through too few VCC and GND pins).