Off Topic: How do PLC backplanes communicate?

Does anyone know how modern PLC backplanes communicate with their IO cards? I assume they are all proprietary but I am guessing they aren’t re-inventing the wheel either.

If someone was to create their own what approach would you use? SPI or UART with individual slot enable lines seems to be the most logical but maybe there is a better way.

Seems to be proprietary for almost all of them. Lots of discussions here.

Thanks for the link. Pretty much confirms what I guessed, everything is proprietary, and figuring out how the hardware is actually communicating is pretty obscure.

If developing an 8-slot rack with a Sitcore I wonder if SPI with 8 chip selects would do the trick.

@Gus_Issa Does TinyCLR support SPI slave?

What kind of data bandwidth would you need? Maybe a CAN or RS485 network might suffice your needs in a bus fashion.

I don’t have a bandwidth estimate yet. This is somewhat of a thought exercise but could move into something more concrete.
I think there is a need for an individual CS, or Slot select, signal for each slot. Each slot needs to work with any style I/O card and multiple of the same I/O card. Because of that, you can’t have a fixed address on the I/O card.
So yes, CAN, RS-485, could be an option but also require the slot select signal. I would think SPI could run faster than either CAN or RS-485, provided the signals can handle the physical distance from the source to the last slot, as well as the loading for 8 I/O cards.