Quote Originally Posted by shawn View Post
I have the software for communicating on the modbus 485 network working but only with a master and one slave. I am getting no bus collisions and all is fine. However I can see in the future that when I get multiple devices on the network my pic is going to be pretty busy dealing with network (bus) traffic and not have a lot of time for anything else.
First of all, you cannot get collisions in a well behaved modbus environment. An occasional hiccup may occur due to false interpretation by multiple slaves. Modbus RTU is typically a master-slave protocol and unless queried, a slave will not reply.

Usually there is only a single master and multiple slaves. This kind of load is easily handled by any PIC with a hardware UART and I do not think you need another comms processor for that.

If you are trying to do a peer-peer network which is also called a multi-master topology, you can anticipate collisions to be the norm. For this, you need to implement CSMA/CD on your PIC. Again, this is no big deal for a microcontroller running reasonable baud rates like 9600/19200.

For the small packet sizes you talk of, I do not think you need bother with the comms processor for your CPU.

This is my way of thinking. YMMV

Cheers