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2 Protocol description
2.1 Master-Slave principle
Communication between a master (e.g. PC) and a slave (e.g. measuring and
control system) using Modbus takes place according to the master-slave
principle, in the form of 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 is
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 data format options are available:
Master
Slave 1 Slave 2 Slave n
Data word Parity bit Stop bit
1/2 bit
Number of
bits
8 bits — 1 9
8 bits even 1 10
8 bits odd 1 10
8 bits — 2 10
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