Communication
2.3 Modbus communication
SIMOCODE pro - Communication
Function Manual, 11/2018, A5E40508495002A/RS-AC/003
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2.3
Modbus communication
2.3.1
Modbus RTU communication
2.3.1.1
Modbus RTU - general
Modbus RTU (Remote Terminal Unit) is a standard protocol for network communication and
uses the electrical RS485 connection for serial data transmission between Modbus devices
in the network.
Modbus RTU uses a master/slave network in which the entire communication is triggered by
only one master device while the slaves can only respond to the request of the master. The
master sends a request to a slave address and only this slave address responds to the
command (exception: broadcast frames to slave address 0 which are not acknowledged by
the slaves).
2.3.1.2
Supported data transfer rates for RTU
SIMOCODE pro supports the following data transfer rates in Modbus RTU mode:
●
300 baud
●
600 baud
●
1,200 baud
●
2,400 baud
●
4,800 baud
●
9,600 baud
●
19,200 baud (default setting)
●
57,600 baud.
2.3.1.3
Assignment of SIMOCODE data to Modbus addresses with Modbus RTU
All SIRIUS data are available in datasets or in the process image:
●
System datasets
●
Datasets specific to a device subfamily
●
Product-specific datasets.
To be addressable via Modbus, the data in these datasets or in this process image are
converted to Modbus data formats.
Data access to
Data type according to Modbus nomenclature
Read-only bits
Discrete inputs
Read/write bits
Coils
Read-only datasets and words (16-bit)
Input registers
Read/write datasets and words
Holding registers
1 coil corresponds to 1 bit.
1 register corresponds to 1 word (2 bytes).
