simple serial one-to-multi protocol (Server to multi clients)

Question

I need a simple communication protocol between multiple devices (a server having one serial port RS-485 connected to few clients). The Server acts as concentrator and sends requests to a specific client. The client will reply to the requests and send sometime some notifications. The operation in general is asynchronous, data payload is a few hundreds of bytes, distances are too near where the time is none critical.

Is there any standard solution for a such situation? (I need only a clue for a start).

Answer 1

Modbus is a common standard, it involves up to 254 clients with many read/write registers each on one RS485 bus. But clients can't send notification without these being queried.