1、Content Introduction
This article mainly introduces the Modbus RTU communication between two Schneider M200 PLCs.
2、Communication Preparation Work
1. Connection Schematic
2. Communication Parameters
3、Master Station Reads Slave Station Program Writing
1. Program Writing
The master station reads 5 words from the slave station using the function block “%READ_VAR0”.
2. Instruction Explanation
Link:1-SL1: Indicates that the port we are using is theM200 main body’sSL1 serial port
Id:3 Indicates that we are reading data from the slave address“3”.
ObjType：0 MW storage area data, using data type “0”
I storage area data, using data type“1”
Q storage area data, using data type“2”
IW storage area data, using data type“3”
FirstObj：100 Indicates that data is read starting from theMW100 data area of the slave station
Quantity：5 Indicates that the number of data is5
Index_Data:50 Indicates that the data read from the slave station is stored in the master stationMW50 starting data area
4、Master Station Writes Slave Station Program Writing
1. Program Writing
The master station writes 5 words to the slave station using the function block “%WRITE_VAR0”.
2. Instruction Explanation
Link:1-SL1: Indicates that the port we are using is the M200 main body’s SL1 serial port
Id:3 Indicates that we are writing data to the PLC with slave address “3”
ObjType：0 MW storage area data, using data type “0”
Q storage area data, using data type “2”
FirstObj：250 Indicates that data is written starting from the MW250 data area of the slave station
Quantity：5 Indicates that the number of data is 5
Index_Data:200 Indicates that the content of the MW200 data area from the master station is prepared to be written to the slave station
5、Case Explanation
If the slave station used on-site is a sensor that supports Modbus RTU, it can be configured to the correspondingcommunication rate, as we have set the TimeOut to 100, which is in units of 100ms, so the total is 10s.
If the line is disconnected, the master station will send data every 10s to look for the slave station. When the on-site slave station or sensor needs to be replaced, the master station will automatically recognize and continuecommunication.
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