I have to read datas from some devices connected through a RS485-USB serial communication cable. The devices use modbus RTU except for one that uses modbus ASCII.
Can I speak two protocols on the same cable? I think RTU units do not reply to ASCII requests and vice-versa, but may this lead to problems? Does anyone tried this or had any experience?
I don't have any device here to try and I have to setup everything directly at client's place.
This would be my ideal configuration
PC_USB----------RS485+RTU------RS485+RTU------RS485+RTU------RS485+ASCII
If this doesn't work I'll have to switch to a solution like the following
PC_USB----------RS485+RTU------RS485+RTU------RS485+RTU
PC_USB----------RS485+ASCII
that would be very problematic due to some constraints on hardware, cables and location.
the short answer is yes. You can speak as many protocols as you want on RS485 as long the messages doesn't get ambiguous.
I have many PV inverters on a shared RS485 line and many other sensors which speak a complete different protocol. The two class of devices share the same line with no problem.