WHAT IS MODBUS RTU

MODBUS RTU is a very popular industry standard protocol. MODBUS RTU uses a standard RS232C/RS485 bus

The MODBUS protocol specifies one master and up to 247 slaves on a common communication line, each slave is assigned a fixed unique device address in the range 1 to 247. The master always initiates a transaction. Transactions are either a query/response type ( only a slave is accessed at a time ) or a broadcast/no response type ( all slaves are accessed at the same time). A transaction comprises a single query and a single response frame or a single broadcast frame.

Frame syncronization is mainteined in RTU transmission mode only by simulating a syncronous message. The MODBUS protocol uses a timeout to determine the completion of the frame. This parameter is often called EOF (End Of Frame).