Modbus Reader Documentation

Module ID: 0cb1e9b3-e809-4f7d-b67c-5a430d267909 Version: 7.2.0 Retrieved: 2025-10-09 15:16:04

Modbus Reader

The module is used to read values from a modbus slave. Several values can be grouped together in the same reader by adding several values to the list of tags to read.

Settings

In the settings you specify the address and port of the modbus slave. The PLC and corresponding tags are imported from a predefined resource. When selecting the PLC you will see all tags that will be read, and you can complement this set by adding your own tags. You can also specify the byte order of the input data.

Name	Requirements	Purpose	Default
IP Address		The modbus slave to connect to	-
Disable module if no IP address is specified	bool	If true the flow will not attempt to start the module if no IP Address is configured	false
Port	number	The port to use when connecting to the slave	502
Use shared connection	bool	If checked, the module will use the same connection as other Modbus modules using shared connections and the same IP.	false
Target Property	String with length 1-64	The property to write the result into. Note that dot-notation is allowed to write the result into a sub-object.	data
Tags collection (Resource)		The resource that contains all tags to read.
Additional tags to monitor		An input table for extra tags to read.
Timeout Settings		See separate Timeout Settings section
Byte Order		The byte order of the input data.	BigEndian

Resource Format

Example of the resource file format.

{
	"name": "SimPLCv3-250",
	"unitId": "1",
	"tags": [
		{
			"id": "Reg0",
			"name": "Reg0",
			"modbusDataType": "UShort",
			"modbusFunction": "ReadHoldingRegisters",
			"address": "0000",
			"unitId": "2"
		}
	]
}

The properties of the tags are described in the following Additional tag properties section.

In addition to these properties, any number of extra fields can be added for each tag when defining tags in the Tags collection resource file. Those fields are then added to the output messages. Use this to add additional metadata associated with each tag.

Additional tag properties

Name	Requirements
Id	String with min length 1. Needs to be unique within all tags
Name	Optional string. If not specified, 'name' = 'id'.
DataType	A valid Modbus tag datatype
Function	A valid Modbus function
Address	In Hex format
BitPosition	Bit position in the register (only for bit)
Length	The number of registers. Only valid for String DataType. Valid range: 1-125 . Most modbus implementations use 2 chars per register
UnitId	If set, this unit id is used for the tag. If not set the default unit id will be used

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

Byte Order

The byte order of the input data can be specified in the settings. The following options are available:

Name	Description	Example
BigEndian	High order byte first.	ABCD
BigEndianWithByteSwap	Big Endian with byte swap.	BADC
LittleEndian	Low order byte first.	DCBA
LittleEndianWithByteSwap	Little Endian with byte swap.	CDAB

Input

Any message can be used to trigger a read operation from the PLC.

Output

Each tag will be added to an array assigned to the Target property. Each object of the array will contain the following properties:

Name	Type	Description
id	string	The tag to read from the modbus slave.
name	string	The friendly name set to the tag.
value	object	The value/result from the modbus slave for the specific tag
unitId	string	The unit id in hex used for the specific tag

# Output

{
    "crosser": {
        "success": true
    },
    "data": [
        {
            "id": "test1",
            "name": "test1",
            "value": 32041,
            "unitId": "1"
        },
        {
            "id": "test2",
            "name": "test2",
            "value": 2
            "unitId": "25"
        },
        {
            "id": "id3",
            "name": "double",
            "value": 125.63,
            "unitId": "AF"
        }
    ]
}

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