Modbus Writer Documentation

Version: 3.0.0 

Retrieved: 2025-10-09 15:16:04

Modbus Writer

The module is used to write values to a modbus slave. The module will write values when a message is received from a previous module and then pass the result to the next module(s) in the flow.

Settings

Name Requirements Purpose Default
IP String with length 1 to 39 IP Address of the PLC to use.  
Port Number 1 to 65000 Port of the PLC to use 502
Use shared connection Boolean If checked, the module will use the same connection as other Modbus modules using shared connections and the same IP. false
Source Property String with length 1 to 64 The property that contains the value to write data
Use Tag Specification from Message Boolean If not checked the Tag Specification has to be set in settings false
Tag Specification See below    

Tag Specification

The data types for the properties on the tag object are described below. They are expected to be set on a property modbus in the message.

Name Requirements
unitId Address of the device to write to in byte 0 - 255
dataType One of (Bool, Byte, Short, UShort, Int, UInt, Long, ULong, Float, Double, String)
function One of (WriteCoils, WriteHoldingRegisters)
startAddress Address 0 - 65535
writeSingleRegisters Bool Should each register be written on at the time (WriteSingleRegisters function used)
byteOrder BigEndian, LittleEndian, BigEndianWithByteSwap or LittleEndianWithByteSwap

Note

The combination of dataType, function and byteOrder is validated. Bool can only be used with WriteCoils and vice versa. WriteHoldingRegisters can be used with all types but Bool.

Timeout Settings

Name Requirements Purpose Default
Read/Write Timeout (milliseconds). Number larger than or equal to 0. The read/write timeout before the communication will fail. 0 means infinite. 60000
Retries. Number larger than or equal to 0. The number of retries to communicate before communication will fail. 0
Wait Between Retries (milliseconds). Number larger than or equal to 0. The number of milliseconds to wait between each communication retry. 0
Status Busy Uses Retry Count. Boolean (true/false). If true status busy from the Slave will be included in retry count. false

Examples

Example with passing only value on input message

# Settings:
IP Address = 192.168.2.15
Port = 502
Use shared connection = false
Source Property = data
Use Tag Specification from Message = false
Tag Specification:
    unitId = 1
    dataType = Short
    function = WriteHoldingRegisters
    startAddress = 0
    writeSingleRegisters = false
    byteOrder = 01

# Incoming message:

{
    data : 123
}

# Outgoing message:

{
    data : 123,
    crosser : {
        success : true
    }
}

Example with passing value and Tag Specification on input message

# Settings:
IP Address = 192.168.2.15
Port = 502
Use shared connection = false
Source Property = data
Use Tag Specification from Message = true

# Incoming message:

{
    data : 123,
    modbus: {
        unitId: 1,
        dataType: 'Short',
        function: 'WriteHoldingRegisters',
        startAddress: 0,
        writeSingleRegisters: false,
        byteOrder: '01',
    }
}

# Outgoing message:

{
    data : 123,
    modbus: {
        unitId: 1,
        dataType: 'Short',
        function: 'WriteHoldingRegisters',
        startAddress: 0,
        writeSingleRegisters: false,
        byteOrder: '01',
    },
    crosser : {
        success : true
    }
}

Output

Output will be the same as the input including a crosser object that reports if the operation was a success or not.

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