ModbusFB Library Problems

Engineering 🇬🇧
matthew
2022-02-18
2022-02-19

  • matthew - 2022-02-18

    Hi,

    I'm having a few issues with the ModbusFB Library. I'm trying to create some reusable function blocks for devices I use quite often. The below is just a simple Modbus Relay board with 2x Inputs and 2x Relay Outputs.

    My Function blocks works with one SerialClient connection, as soon as I link the second ClientSerial to the second FB I get error 56 which is reply timeout. Both FBs work if I connect each one independantly, just can't have both connected together.

    [-img src=CodeSys ModbusFB Issue.png width=50%: missing =-]

    Here is the ClientSerial ModbusFB 

    FUNCTION_BLOCK Modbus_Client_Serial
VAR_INPUT
    //Serial Client Setup
    ComPort   : INT;
    BaudRate  : DWORD;
    DataBits  : BYTE;
    Parity    : BYTE;
    StopBits  : BYTE;
    RtuAscii  : ModbusFB.RtuAscii;
    xConnect  : BOOL;
    //Auto Reconnect Until Device Found
    AutoReconnect : BOOL;
    //Reset 
    Reset : BOOL;

END_VAR

VAR_IN_OUT  
    //Connect Client Between ModbusFBs
    ClientSerial : ModbusFB.ClientSerial;
END_VAR 

VAR_OUTPUT
    //Errors from FBs
    Error    : BOOL;
    ErrorID  : INT;

END_VAR
VAR
    initDone : BOOL;
    ClientConnected : BOOL;
    ClientErrorCnt : UINT;
    CasePos : INT;

END_VAR

    Here is the code 

    //This FB Uses SysCom please see CodeSys ModbusFB for more information

IF NOT initDone THEN
    //First Scan
    initDone := TRUE;
    CasePos := 0;
END_IF;

//Call Client 
ClientSerial();
//Check Client is Connected
ClientConnected := ClientSerial.xConnected;

CASE CasePos OF

0: //Step 0 Setup Serial Client
    ClientSerial(   
        iPort:= ComPort, 
        dwBaudrate:= BaudRate, 
        byDataBits:= DataBits, 
        eParity:= Parity, 
        eStopBits:= StopBits,  
        eRtuAscii:= RtuAscii);
    CasePos := 10; //Move to step 10 to setup Client Connect  

10: //Step 10 Connect The Client
    IF xConnect THEN
        ClientSerial.xConnect :=TRUE;
    ELSE 
        ClientSerial.xConnect :=FALSE;
    END_IF


    IF ClientSerial.xError OR ClientSerial.eErrorID > 0 THEN
        CasePos := 1000; // Process Error
    END_IF

1000: //Step 1000 Process Errors
    //Process Client Connection Errors
    IF ClientSerial.xError OR ClientSerial.eErrorID > 0 THEN

        IF AutoReconnect THEN
            //Errors from the Client Functions Reset The Client and repeat until no error ( No Error Flag Active )
            ClientSerial.xConnect := FALSE;
            CasePos := 10; // Try to reconnect the client 
        ELSE 
            IF ClientErrorCnt < 5 THEN
                //Try to reconnect the client 5x then create error flag
                ClientSerial.xConnect := FALSE;
                ClientErrorCnt := ClientErrorCnt + 1;
                CasePos := 10; // Try to reconnect the client
            ELSE  
                //Set Error to TRUE and display ErorrID 
                Error := TRUE;
                ErrorID := ClientSerial.eErrorID;
                ClientSerial.xConnect := FALSE;

                IF Reset THEN 
                    Error := FALSE;
                    ErrorID := 0;
                    ClientErrorCnt := 0;
                    CasePos := 0; //Reset Serial Client Parameters incase of changes 
                END_IF
            END_IF
        END_IF
    END_IF


END_CASE

    Here is the Relay Board Code

    FUNCTION_BLOCK Modbus_Relay_x2
VAR_INPUT

    //Slave Address ID
    UnitID    : UINT;
    //Auto Reconnect Until Device Found
    AutoReconnect : BOOL;
    //Reset 
    Reset : BOOL;
    //Relay Control
    Relay_1_On : BOOL;
    Relay_2_On : BOOL;

END_VAR

VAR_IN_OUT  
    //Connect Client Between ModbusFBs
    ClientSerial : ModbusFB.ClientSerial;
END_VAR 

VAR_OUTPUT
    //Errors from FBs
    Error    : BOOL;
    ErrorID  : INT;
    //Optocoupler Inputs
    Input_1_Status  : BOOL;
    Input_2_Status  : BOOL;

END_VAR
VAR
    initDone : BOOL;
    ClientConnected : BOOL;
    ErrorCnt : UINT;
    FbErrorID : INT;
    DataCoils_Inputs : ARRAY [0..7] OF BOOL;
    Relay1_FC05: ModbusFB.ClientRequestWriteSingleCoil;
    Relay2_FC05: ModbusFB.ClientRequestWriteSingleCoil;
    Inputs_FC02: ModbusFB.ClientRequestReadDiscreteInputs;  

    CasePos : INT;

END_VAR

    Here is the Code

    //This FB Uses SysCom please see CodeSys ModbusFB for more information

IF NOT initDone THEN
    //First Scan
    initDone := TRUE;
    CasePos := 0;
END_IF;

ClientConnected := ClientSerial.xConnected;

CASE CasePos OF

0: //Step 0 Initiate Functions
    //Setup Relay 1 ( Address offset 0 )
    Relay1_FC05(  
        rClient:= ClientSerial, 
        uiUnitId:= UnitID,  
        uiItem:= 0);

    //Setup Relay 2 ( Address offset 1 )    
    Relay2_FC05(  
        rClient:= ClientSerial, 
        uiUnitId:= UnitID,  
        uiItem:= 1);

    //Setup Optocoupler Inputs ( Store Bits in an Array )
    Inputs_FC02(  
        rClient:= ClientSerial, 
        uiUnitId:= UnitID, 
        uiStartItem:= 0, 
        uiQuantity:= 8, 
        pData:= ADR(DataCoils_Inputs[0]));
    CasePos := 20; //Begin Processing Modbus Data

10: //Step 10 Reconnect SerialClient
    ClientSerial.xConnect := TRUE;

    IF ClientSerial.xConnected THEN
        CasePos := 20; 
    ELSE
        CasePos := 1000; //Client failed to connect move to errors
    END_IF 


20: //Step 20 Process Relay 1 ( Modbus Function Code 05 )
    IF ClientConnected AND NOT Relay1_FC05.xExecute THEN 
        Relay1_FC05.xExecute := TRUE;

    END_IF;

    IF Relay1_FC05.xExecute THEN

        IF Relay1_FC05.xBusy THEN
            Relay1_FC05.xExecute := FALSE;
        END_IF;

        IF Relay_1_On THEN
            //Coil Write ( Turn on Relay 1 )
            Relay1_FC05(xValue:= TRUE,
                rClient := ClientSerial);
        ELSE
            //Coil Write ( Turn off Relay 1 )
            Relay1_FC05(xValue:= FALSE,
                rClient := ClientSerial);    
        END_IF; 
        //Move to next Data Set 
        IF Relay1_FC05.xDone THEN
            Relay1_FC05.xExecute := FALSE;
            CasePos := 30; // Relay 2
        END_IF; 
        //Process Errors
        IF Relay1_FC05.xError OR Relay1_FC05.eErrorID > 0 THEN
            Relay1_FC05.xExecute := FALSE;
            FbErrorID := Relay1_FC05.eErrorID;
            CasePos := 1000;
        END_IF
    END_IF;

30: //Step 30 Process Relay 2 ( Modbus Function Code 05 )
    IF ClientConnected AND NOT Relay2_FC05.xExecute THEN 
        Relay2_FC05.xExecute := TRUE;
    END_IF;

    IF Relay2_FC05.xExecute THEN

        IF Relay2_FC05.xBusy THEN
            Relay2_FC05.xExecute := FALSE;

        END_IF;

        IF Relay_2_On THEN
            //Coil Write ( Turn on Relay 2 )
            Relay2_FC05(xValue:= TRUE,
                rClient := ClientSerial);
        ELSE
            //Coil Write ( Turn off Relay 2 )
            Relay2_FC05(xValue:= FALSE,
                rClient := ClientSerial); 
        END_IF; 
        //Move to next Data Set 
        IF Relay2_FC05.xDone THEN
            Relay2_FC05.xExecute := FALSE;
            CasePos := 40; // Opto Inputs
        END_IF; 
        //Process Errors
        IF Relay2_FC05.xError OR Relay2_FC05.eErrorID > 0 THEN
            Relay2_FC05.xExecute := FALSE;
            FbErrorID := Relay2_FC05.eErrorID;
            CasePos := 1000;
        END_IF
    END_IF;

40: //Step 40 Process Inputs ( Modbus Function Code 02 )
    IF ClientConnected AND NOT Inputs_FC02.xExecute THEN 
        Inputs_FC02.xExecute := TRUE;

    END_IF;

    IF Inputs_FC02.xExecute THEN

        IF Inputs_FC02.xBusy THEN
            Inputs_FC02.xExecute := FALSE;
        END_IF;
        //Read Coils from Optocouplers
        Inputs_FC02(rClient := ClientSerial); 

        IF Inputs_FC02.xDone THEN
            Inputs_FC02.xExecute := FALSE;
            //Read The Status of the Inputs
            Input_1_Status := DataCoils_Inputs[0];
            Input_2_Status := DataCoils_Inputs[1];
            CasePos := 20; // Return to the start of the stack
        END_IF; 
        //Process Errors
        IF Inputs_FC02.xError OR Inputs_FC02.eErrorID > 0  THEN
            Inputs_FC02.xExecute := FALSE;
            FbErrorID := Inputs_FC02.eErrorID;
            CasePos := 1000;
        END_IF
    END_IF;


1000: //Step 1000 Process Errors

    IF AutoReconnect THEN
        //Errors from the Modbus Functions Reset The Client and repeat until device found ( No Error Flag Active )
        ClientSerial.xConnect := FALSE;
        CasePos := 10; // Try to reconnect the client 
    ELSE 
        IF ErrorCnt < 5 THEN
            //Try to resolve the Error 5x then create Error Flag
            ClientSerial.xConnect := FALSE;
            ErrorCnt := ErrorCnt + 1;
            CasePos := 10; // Try to reconnect the client
        ELSE 
            //Set Error to TRUE and display ErorrID 
            Error := TRUE;
            ErrorID := FbErrorID;
            ClientSerial.xConnect := FALSE;

            IF Reset THEN 
                Error := FALSE;
                ErrorID := 0;
                ErrorCnt := 0;
                CasePos := 10; //Reconnect Client
            END_IF
        END_IF
    END_IF          



END_CASE

    I have also tested using the original ModbusFB.ClientSerial Function Block and I get the exact same results. I have tried with 2x ClientSerial for each function block and still get the same error. Seems like I can only use 1x ClientSerial with 1x Function Block

     
    Thumbnail
    CodeSys ModbusFB Issue.png

  • dFx

    dFx - 2022-02-18

    You cannot execute 2 functions at the same time on the same port. You have to sequence each request.

    I would call the read/write inside the MODBUS_CLIENT_SERIAL and then provide a queue for the MODBUS_RELAY FBs. Then just place a request with its parameters in the queue with MODBUS_RELAY, process them in MODBUS_CLIENT_SERIAL, using pointers for in/out data, and also results. This way the asking RELAY FB could be aware his request have been processed.

    For less modifications of your code, you can also add a flag that the line is currently busy, but you will have to manage RELAY FBs concurrency.

     

    Last edit: dFx 2022-02-18

    • matthew - 2022-02-18

      Hi dFx,

      Thanks, that makes perfect sense and I should have picked up on that one. Would you have an example of setting up a queue with the pointers? I haven't used pointers or anything like that before so wouldn't know where to start. I'm trying todo it dynamically so I can easily add more of the same devices or different devices in the future without much modification to the project.

       

      • dFx

        dFx - 2022-02-18

        Pointers are not a big deal. See help
        For instance, you may have a struct, for the queue elements.
        Lets say you need to know the type of work (read/write), the data to be written or read.

        STRUCT ModbusQueueItem
    TypeOfWork : INT;
    pData : Pointer TO BOOL; // Data pointer for boolean data
    szData : INT; // Size of data
END_STRUCT

        So In case of Read, just provide the pData to pData of ClientRequestReadDiscreteInputs, given that your RELAY block did correctly set the item using ADR(YourData).

        This is only a draft, not real code, so there maybe adjustements to do on types.

         

        • matthew - 2022-02-19

          Hi dFx,

          Can you not pass the whole struct as an In/Out and every FB have a connection to that struct?
          What I'm thinking is every slave already has an unique ID/Address and in the Modbus_Client_Serial FB having a FOR loop looking for these IDs may have 8 devices all with different addresses and store them in an array and then use another FOR loop based on the size of that array to trigger the slave devices in sequence based on there address and when that device FB is done it goes on to the next device FB? I haven't dealt with comms stuff in the past and the correct way todo this.

           

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