Set_Modbus_Holding_Registers

Overview

The Set_Modbus_Holding_Registers function block writes values from a local data array into the PLC Modbus Holding Register map. The following steps are required to correctly use the function block:

Select the starting Modbus register
Define the number of registers to write
Select the starting index inside the source DATA array
Provide the DATA array containing the values to be written

💡 Array Size Limitation

The DATA input array has a fixed size of 100 elements (0..99). Make sure MDB_Number_of_registers does not exceed this limit to avoid out-of-bounds errors.

⚠️ What will trigger a fault on the function block?

The following conditions need to be true, in order to correctly run the function block:

MDB_Number_of_registers must be within the range 0..99 (inclusive)
MDB_Start_Register + MDB_Number_of_registers ≤ 1000
DATA_Start_Element + MDB_Number_of_registers ≤ 100

MDB_Start_Register          := (UINT)
MDB_Number_of_registers     := (UINT)
DATA_Start_Element          := (UINT)
DATA                        := (ARRAY [0..99] OF UINT)
STS_Done                    => (BOOL)
STS_Failed                  => (BOOL)
STS_Fault_Code              => (USINT)

Interface

Inputs

Name	Type	Range / Units	Description
MDB_Start_Register	UINT	0 - 999	Start index in the PLC Modbus holding register table to write to.
MDB_Number_of_registers	UINT	1 - 99	Number of consecutive holding registers to write.
DATA_Start_Element	UINT	0 - 99	Start index inside the source `DATA` array.
DATA	ARRAY[0..99] OF UINT	—	Source buffer containing the values to be written into holding registers.

Outputs

Name	Type	Description
STS_Set_Data_Done	BOOL	`TRUE` when the write completed successfully.
STS_Set_Data_Failed	BOOL	`TRUE` when the operation failed.
STS_Fault_Code	USINT	Diagnostic code indicating the reason for failure.

Status Codes

Code	Meaning	Description
90	Index outside of array bounds	One or more limits were exceeded (max write count, holding register range, or `DATA` range).
91	Unknown error	Unknown error occurred during operation.

Example

PROGRAM PROG_Set_Ethernet_Config
    VAR
        EthCfg : SET_ETHERNET_CONFIG;
        _IP_Address : ARRAY [0..3] OF USINT := [192, 168, 11, 2];
        _Subnet_Mask : ARRAY [0..3] OF USINT := [255, 255, 255, 0];
        _Gateway : ARRAY [0..3] OF USINT := [192, 168, 11, 1];
        _DNS : ARRAY [0..3] OF USINT := [8, 8, 8, 8];
    END_VAR

    EthCfg(
        Network_Operation_Mode := 1,                
        IP_Allocation_Method   := 0,                
        IP_Address             := _IP_Address,
        Subnet_Mask            := _Subnet_Mask,
        Gateway                := _Gateway,
        DNS                    := _DNS,
        Port                   := 5000
    );
END_PROGRAM

PROGRAM PROG_Set_Modbus_HR
    VAR
        WriteHR : SET_MODBUS_HOLDING_REGISTERS;
        SrcData : ARRAY [0..99] OF UINT := [10, 11, 12, 13, 14, 15, 16, 17, 18, 19];
    END_VAR

    SrcData[9] := SrcData[9] + 1;
    WriteHR(
        MDB_Start_Register      := 0,
        MDB_Number_of_registers := 10,
        DATA_Start_Element      := 0,
        DATA                    := SrcData
    );
END_PROGRAM

CONFIGURATION Config0
    RESOURCE Res0 ON PLC
        TASK task1_20ms(INTERVAL := T#20ms, PRIORITY := 1);
        PROGRAM Prog_Instance_SET_ETHERNET_CONFIG WITH task1_20ms : PROG_Set_Ethernet_Config;
        PROGRAM Prog_Instance_SET_MODBUS_HR WITH task1_20ms : PROG_Set_Modbus_HR;
    END_RESOURCE
END_CONFIGURATION