User Manual

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2 Protocol description
2.1 Master-slave principle
The communication between a PC (master) and a device (slave) using
MODbus takes place according to the master-slave principle, in the
form of a data request/instruction - response.
The master controls the data exchange, the slaves only have a
response function. They are identified by their device address.
2.2 Transmission mode (RTU)
The transmission mode used is the RTU mode (Remote Terminal Unit).
Data are transmitted in binary format (hexadecimal) with 8 bits. The LSB
(least significant bit) is transmitted first. The ASCII operating mode is
not supported.
Data format
The data format describes the structure of a character transmitted. The
following format options are available:
Master
Slave 1 Slave 2 Slave n
Data word Parity bit Stop bit
1/2 bit
Bit
number
8 bit — 1 9
8 bit even 1 10
8 bit odd 1 10
8 bit — 2 10