Modbus RTU Read Works But Write Doesn't

Hello everybody,

I am trying to read and write data from a Deye Inverter to an AXC F 2152 PLC using a RS485 Module for Modbus RTU communication. I am also using the Modbus RTU 15 Library.

With the current setup I am able to read data from the Deye inverter. The code I use for this is as follows:

 CASE Inverter_RTU.iStateInverter OF

    0: (* Wait for xStart *)

        IF xStartInverter = TRUE THEN

            Inverter_RTU.iStateInverter := 10;

        END_IF;

    10: (* Start Master *)

        Inverter_RTU.udtMB_RTU_FC3.xActivate := FALSE;

        Inverter_RTU.udtMB_RTU_FC3.xSendRequest := FALSE; 

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.tModbus_Timeout := TIME#2s;

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.tPD_Timeout := TIME#2s;

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.xActivate := TRUE;

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.xMode := FALSE;

        Inverter_RTU.iStateInverter := 20;

    20: (* Wait for Master xActive *)

        IF Inverter_RTU.udtMB_AXL_SE_RS485_Master.xError = TRUE THEN

            Inverter_RTU.iStateInverter := 10;

        ELSIF Inverter_RTU.udtMB_AXL_SE_RS485_Master.xActive = TRUE THEN 

            Inverter_RTU.iStateInverter := 30;

        END_IF;

    30: (* Activate FC3 *)

        Inverter_RTU.udtMB_RTU_FC3.xActivate := TRUE;

        Inverter_RTU.udtMB_RTU_FC3.xSendRequest := FALSE;

        Inverter_RTU.udtMB_RTU_FC3.uiSlaveAddress := UINT#1;

        Inverter_RTU.udtMB_RTU_FC3.xEnablePoll := FALSE;

        Inverter_RTU.udtMB_RTU_FC3.tPollInterval := T#0.5s;

        Inverter_RTU.udtMB_RTU_FC3.uiStartAddress := UINT#0;

        Inverter_RTU.udtMB_RTU_FC3.iDataCount := 125;

        IF Inverter_RTU.udtMB_RTU_FC3.xError = TRUE THEN

            Inverter_RTU.iStateInverter := 10;

        ELSIF Inverter_RTU.udtMB_RTU_FC3.xActive = TRUE AND Inverter_RTU.udtMB_RTU_FC3.xBusy = FALSE THEN

            Inverter_RTU.iStateInverter := 40;

        END_IF; 

    40: (* Start sendrequest FC3 *)

        Inverter_RTU.udtMB_RTU_FC3.xSendRequest := TRUE;    

        IF Inverter_RTU.udtMB_RTU_FC3.xError = TRUE THEN

            Inverter_RTU.udtMB_RTU_FC3.xActivate := FALSE;

            Inverter_RTU.udtMB_RTU_FC3.xSendRequest := FALSE; 

            Inverter_RTU.iStateInverter := 30;

        ELSIF Inverter_RTU.udtMB_RTU_FC3.xActive = TRUE AND Inverter_RTU.udtMB_RTU_FC3.xBusy = FALSE AND Inverter_RTU.udtMB_RTU_FC3.xDone = TRUE THEN

            runState := Inverter_RTU.udtMB_RTU_FC3.arrReadData[63];

            Inverter_RTU.udtMB_RTU_FC3.xSendRequest := FALSE;

            Inverter_RTU.udtMB_RTU_FC3.xActivate := FALSE;

        END_IF; 

This code works and gives me the data I need. However, when I am trying to write to the Deye Inverter I get the error 16#C110 Modbus error: 16#0001 Modbus communication timeout from the FC6 function block. I have written the following code for a write request:

 CASE Inverter_RTU.iStateInverterWrite OF

    0: (* Wait for xStart *)

        IF xStartInverterWrite = TRUE THEN

            Inverter_RTU.iStateInverterWrite := 10;

        END_IF;

    10: (* Start Master *)

        Inverter_RTU.udtMB_RTU_FC6.xActivate := FALSE;

        Inverter_RTU.udtMB_RTU_FC6.xSendRequest := FALSE; 

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.tModbus_Timeout := TIME#2s;

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.tPD_Timeout := TIME#2s;

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.xActivate := TRUE;

        Inverter_RTU.udtMB_AXL_SE_RS485_Master.xMode := FALSE;

        Inverter_RTU.iStateInverterWrite := 20;

    20: (* Wait for Master xActive *)

        IF Inverter_RTU.udtMB_AXL_SE_RS485_Master.xError = TRUE THEN

            Inverter_RTU.iStateInverterWrite := 10;

        ELSIF Inverter_RTU.udtMB_AXL_SE_RS485_Master.xActive = TRUE THEN 

            Inverter_RTU.iStateInverterWrite := 30;

        END_IF;    

    30: (* Prepare to send request *)

        Inverter_RTU.udtMB_RTU_FC6.xActivate := TRUE;

        Inverter_RTU.udtMB_RTU_FC6.xSendRequest := FALSE;

        Inverter_RTU.udtMB_RTU_FC6.uiSlaveAddress := UINT#1;

        Inverter_RTU.udtMB_RTU_FC6.xEnablePoll := FALSE;

        Inverter_RTU.udtMB_RTU_FC6.tPollInterval := T#0.5s;

        Inverter_RTU.udtMB_RTU_FC6.uiStartAddress := UINT#62;

        Inverter_RTU.udtMB_RTU_FC6.wValue := WORD#2510;

        IF Inverter_RTU.udtMB_RTU_FC6.xActive = TRUE AND Inverter_RTU.udtMB_RTU_FC6.xBusy = FALSE THEN

            Inverter_RTU.iStateInverterWrite := 40;    

        END_IF; 

    40: (* Send the request *)

        Inverter_RTU.udtMB_RTU_FC6.xSendRequest := TRUE;

END_CASE;

iStateInverterWrite := Inverter_RTU.iStateInverterWrite;

As you can see both codes are almost identical in logic and flow except for the function block I am using. I do not understand why I get an error. I believe that since I can read holding registers the issue is not hardware based but software based.

I am sure the slave adress, holding register and register value I am trying to write to are correct. I have tried different values for all that should or should not work but I keep getting the same error. I have attached the documentation of the register below.

I am also very new to PLC programming so maybe I am not seeing something obvious. Any help to solve this problem will be appreciated greatly😀.

Kind Regards, Rutger