Modbus/RTU
What you will find in this section:
Modbus/RTU
In the case of Modbus/RTU, the Modbus application layer protocol is supplemented with additional information and physically sent via an RS-485 interface. The start and end of a Modbus message is coordinated by means of timings.
Modbus/RTU describes a client/server protocol. Normally, the EMpro acts as Modbus/RTU server. An exception here is the gateway mode.
The additional information consists of a byte for addressing the device. Valid device addresses are in the range from 1-247.
The default setting for the devices is address 1. Address 0 is reserved for broadcast messages in the network and cannot be assigned as an address to a device.
According to the specification, addresses 248-255 are reserved and cannot be assigned to the device either.
A cyclic redundancy check (CRC) is attached to the Modbus message as additional information. The CRC is used to detect transmission errors. The calculation and the polynomial used are documented in the Modbus specification.
The Modbus/RTU protocol is supported by all EMpro versions with an RS-485 interface.
Configuration
|
Function |
Information |
Web server |
Display |
Register |
|
Activation of Modbus/RTU |
The Modbus/RTU protocol is activated by default, but can be deactivated by the user. |
x |
x |
x |
|
Modbus address |
The default setting is address 1. |
x |
x |
x |
|
Baud rate |
The default setting for the RS-485 interface is 9600 bps. |
x |
x |
x |
|
Stop bits |
The default setting for the RS-485 interface is 1 stop bit. |
x |
x |
x |
|
Parity |
The default setting for the RS-485 interface is even parity. |
x |
x |
x |
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