I've set up an RS485 network with 4 nodes + my computer, which communicates via a USB-to-RS485 unit. The nodes are PIC16F345 processors, each with a MAX485 transceiver chip. It all works well in master-slave mode, with the computer as master, initiating every exchange. Now I'm wondering how difficult it would be to run the network as a token-passing system not requiring a computer. I've tried to find out whether anyone has done this before, in a minimal manner. It seems that token-passing schemes are quite complicated, and I don't want to use much of the processors' resources for this. How simple could a setup be, and still function robustly? It would need to start itself up, allow for nodes entering or leaving the bus, handle corrupted attempts at token-handling, and no doubt some other requirements I haven't thought of.
First of all, has this particular wheel been invented yet? I'd have thought that someone would have felt motivated to do it--but maybe it turns out to be so complex that a small processor can't handle it. Please don't say "Modbus"; that's master-slave only.
Second, is there any publication (preferably online) which describes the full requirements for such a system? If it hasn't been done already, I'd at least like to understand the features that a working system would need to have. Maybe then I'd decide that it's not worth trying, but at least I'd know why.
Here's my 4-node setup, with unit 25 controlling a couple of hobby servos, a reset switch on unit 40, and power to drive all the processors coming in on unit 26. The boards are meant to be linked by RJ12 connectors and cables, but I didn't have enough hardware to do it that way, so there are some other wires installed.
First of all, has this particular wheel been invented yet? I'd have thought that someone would have felt motivated to do it--but maybe it turns out to be so complex that a small processor can't handle it. Please don't say "Modbus"; that's master-slave only.
Second, is there any publication (preferably online) which describes the full requirements for such a system? If it hasn't been done already, I'd at least like to understand the features that a working system would need to have. Maybe then I'd decide that it's not worth trying, but at least I'd know why.
Here's my 4-node setup, with unit 25 controlling a couple of hobby servos, a reset switch on unit 40, and power to drive all the processors coming in on unit 26. The boards are meant to be linked by RJ12 connectors and cables, but I didn't have enough hardware to do it that way, so there are some other wires installed.