Modbus

The Modbus Device component is a Modbus master. It connects to one Modbus slave over Transmission Control Protocol (TCP) or over a serial line using Remote Terminal Unit (RTU) framing, and polls the coils and registers you list in its point map, publishing each one as a Profinity tag. Modbus is used for industrial devices and distributed input/output (I/O). Profinity acts as a Modbus master only, and it does not act as a Modbus slave or server.

flowchart LR
    Slave["Modbus slave"]
    subgraph Profinity
        Component["Modbus Device"] --> Tags
    end
    Slave --> Component

The Modbus Device component in Profinity polls the coils and registers in its point map from one Modbus slave and publishes each as a Profinity tag

Licence required

The Modbus plugin is not part of the standard installation, and it requires the Industrial Protocols licensed component group. Refer to Industrial Protocols for how to obtain, install, and licence it.

Add a Modbus Device to your Profile from the Industrial Protocols group in the component catalogue, as described in Adding Components to Your Profile. Add one component for each slave you want to read. The settings below can be changed later from the component's Change Settings menu action.

Communications settings

Which settings apply depends on the Connection Mode.

Setting	Applies to	Description
Name	Both	The name of the component. Must be unique within the profile.
Connection Mode	Both	`TCP` (the default) or `RTU`.
Host	TCP	The IP address of the slave. Required. The default is `127.0.0.1`.
Port	TCP	The TCP port. Between `1` and `65535`. The default is `502`.
Serial Port	RTU	The serial port the slave is connected to. Required for RTU.
Baud Rate	RTU	The serial baud rate. The default is `9600`.
Parity	RTU	The serial parity. The default is `None`.
Data Bits	RTU	`7` or `8`. The default is `8`.
Stop Bits	RTU	The number of stop bits. The default is `One`.
Unit ID	Both	The Modbus unit (slave) address. Between `0` and `255`. The default is `1`.
Poll interval (ms)	Both	How often the point map is read, in milliseconds. Between `50` and `600000`. The default is `1000`.
Request timeout (ms)	Both	How long Profinity waits for the slave to answer a request, in milliseconds. Between `50` and `60000`. The default is `1000`.
Reconnect delay (ms)	Both	How long Profinity waits between connection attempts, in milliseconds. Profinity keeps trying when the device is down at start and after a connection is lost, as described in Connections and reconnecting. Between `0` and `600000`. The default is `2000`.
Auto Connect	Both	Connects automatically when the profile is loaded. Off by default.

Match the serial settings to those configured on the slave. If they differ, the slave does not answer.

Point map

The point map lists the coils and registers to read. Each row becomes one tag.

Column	Description
Name	The name of the tag, published under the component's `Points` tags. Use a unique name for each row.
Table	The Modbus table to read: `Coil`, `DiscreteInput`, `HoldingRegister` (the default) or `InputRegister`.
Address	The zero-based protocol address. Register `40001` in a manufacturer's manual is address `0` of the holding registers when the manual uses one-based numbering.
Data type	How the value is decoded: `Boolean`, `Word` (the default), `SignedWord`, `Dword`, `SignedDword` or `Real`.
Scale	A factor that reads are multiplied by. Writes are divided by the same factor. The default is `1`.
Writable	Allows Profinity to write the value from the tag. Off by default.
Unit	An optional unit label for the tag.

Registers are read as big-endian values. Word and SignedWord use one register, and Dword, SignedDword and Real use two consecutive registers starting at the address, with the first register holding the high word. The component has no word-swap option, so a device that sends the low word first returns wrong 32-bit values. Real is a 32-bit floating point value.

The Scale suits devices that report fixed-point values: a temperature held as tenths of a degree uses a scale of 0.1.

A Coil or DiscreteInput row always reads a single on/off bit, and its Data type is not used. A Boolean row on a HoldingRegister or InputRegister table reads one register and is true when the register is not zero.

Only the HoldingRegister and Coil tables can be written. DiscreteInput and InputRegister points are always read-only, even if Writable is on.

Writing to a device

Leave Writable off for any point that Profinity should only monitor, because a write changes the device.

Dashboard

The component dashboard shows the connection STATUS (Connected or Disconnected), whether the device is CONNECTED, and the number of values read (RECEIVED) and values written (SENT). Use the Connect / Disconnect menu action to start or stop polling manually. Viewing the dashboard requires the Security administration permission, described under Roles and Permissions.

Polled values behave like any other tag, so they can be shown on a dashboard, logged, watched by a rule, or read by a script.

If a point shows bad quality

If a point cannot be read, its tag is marked as bad quality. The usual causes are an address that is one higher or lower than the device manual states, a Unit ID that differs from the slave, serial settings that differ from the slave, and a Data type that does not match the register. Check these before reading the Log for the reason. The Log records the first failed read of an outage as a warning, repeat failures in the same outage at debug level, and the first success afterwards at information level, as described in Connections and reconnecting. The first success is the first poll in which every point reads correctly.