Multiprocessor Communication via RS485

Well, it is possible to create a bus structure using 485 however you will need to make sure in your protocol not to have conflicts between multiple devices. Many drives incorporate 485 bus communication. Now, with 28335 you may seriously consider other communication port like CAN to create your multiprocessor bus - CAN will inherently be more robust and offers all the required features necessary for a bus configuration.

You can use a 485 driver chip connected to sci. But making a multiple master bus is difficult. You could try a single master bus with a simple command response protocol. One cpu has to be in charge and pole the others. I found it very difficult to switch the tx on the driver chip at the correct time. If you try this I would receive everything you send then wait for the reply, rather than switiching the chip from tx to rx. However CAN is a lot better at this sort of stuff.

I agree with most of the issues you mentioned about using 485 in a bus structure however as I mentioned earlier it is possible to develop a protocol to reduce most if not all the issues. One good item is to incorporate device "ID" in protocol to avoid multiple usnits answering or receiving at the same time. However , as mentioned, CAN should be a better solution.