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2
Protocol description
2.1
Master-Slave principle
C ommunication between a master (e.g. PC) and a slave (e.g. measuring and control
system) using Modbus takes place according to the master-vlave principle, in the
form of data request/instruction - response.
Slave 1
T he master controls the data exchange, the slaves only have a response function.
They are identified by their device address.
2.2
Transmission mode (RTU)
T he 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:
Data Word
8 bits
8 bits
8 bits
8 bits
Master
Slave 2
Parity bit
–
even
odd
–
Slave n
Stop bit ½ bit
1
1
1
2
Number of bits
9
10
10
10
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