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Example

Requirements: Hardware: CPU 1214C - 6ES7 214-1AG40-0XB0, CB1241 - 6ES7 241-1CH30-1XB0

Software: TIA Portal V15.1 or higher

Download TIA-project: link

In the example we read 3 registers from Device1 and write these values to Device2.

Reading data from device Device1 is performed in 2 requests: read 40001, read 40002,40003.

Writing to the Device2 device is performed in one request: writing to 40003, 40004, 40005.

Configuration

Device1

The DB ModbusRtuMaster_DevicesDb.device1 contains the query configuration for Device1.

Request 1 (requests[0]): Read register 40001, place value in device1.buffer[0].

Request 2 (requests[1]): Read register 40002..40003, place values in device1.buffer[1]..device1.buffer[2]

example read

Device2

The DB ModbusRtuMaster_DevicesDb.device2 contains the query configuration for Device2.

Request 1 (requests[0]): Write from device1.buffer[0]..device1.buffer[2] to registers 40003..40005.

example write

Code

The main logic is located in the function block ModbusRtu_Master

example read subroutines

Initializing the serial port

Initialization must occur once when the controller is started; for this, the FirstScan system flag is used.

If initialization is completed successfully, set token to poll the first device (i = 0)

REGION Serial port initialization
     IF "FirstScan" THEN
         #mbCommLoad.MODE := 4;
     END_IF;
    
     #mbCommLoad.RETRIES := #com.retries;
    
     #mbCommLoad(REQ := "FirstScan",
                 "PORT" := #com."port",
                 BAUD := #com.baud,
                 PARITY := #com.parity,
                 MB_DB := #mbMaster.MB_DB,
                 RESP_TO := #com.timeout,
                 DONE => #com.done,
                 ERROR => #com.error,
                 STATUS => #com.status);
    
     #initTrig(CLK := #com.done);
    
     IF #initTrig.Q THEN
         #i := 0;
     END_IF;
END_REGION

Poll Device1

To call instance of FB "LMBMD_ModbusDeviceRtu_Master" you need to send a single pulse to the start input.

#start := NOT #inst_LModbusDeviceRtu_Master.done;

Poll of device Device1 starts.

When all requests is completed the output done will be set to true once.

We start copying data from device1.buffer to DataDb.device (FC "ModbusRtu_Device1_MapData").

Set the next token (i := i + 1).

IF #inst_LModbusDeviceRtu_Master.done THEN
     "ModbusRtu_Device1_MapData"(mdata := "ModbusRtuMaster_DevicesDb".device1,
                                 data := "DataDb".device);
     #i := #i + 1;
END_IF;

//"ModbusRtu_Device1_MapData"
#data.param1 := #mdata.buffer[0];
#data.param2 := #mdata.buffer[1];
#data.param3 := #mdata.buffer[1];

Poll Device2

Before starting polling of Device2, the data to be written is moved from DataDb.device to device2.buffer (FC ModbusRtu_Device2_MapData).

//"ModbusRtu_Device2_MapData"
#mdata.buffer[0] := #data.param1;
#mdata.buffer[1] := #data.param2;
#mdata.buffer[2] := #data.param3;

Poll of device Device2 starts.

When all requests is completed the output done will be set to true once.

Set the next token (i := i + 1)

         IF #inst_LModbusDeviceRtu_Master.done THEN
             #i := #i + 1;
         END_IF;

Tokens have run out, set the initial one and start the process again

     ELSE
         #i := 0;