Modbus Server trigger event

The execution of a trigger can be controlled by the receipt of a Modbus write command processed by the Modbus Server. Clients that interface with the Modbus server can modify coils and holding registers defined on the Modbus Server, using either the Write Single Coil (0x05), Write Single Register (0x06), Write Multiple Coils (0x0F), or Write Multiple Registers (0x10) Modbus commands. A trigger can be defined that will execute whenever the Modbus Server processes any of these commands or when it processes a specific write command. The Modbus Server Write trigger event is found under the PLC Logic Events category of trigger event types.

Modbus Server Write event type trigger

To define a trigger that executes when a Modbus Server Write occurs, select the Modbus Server Write trigger event type. The Event tab becomes active with parameters that accommodate the event type.

Modbus Server Write event type trigger parameters

Parameter	Description
Device Name	Select the name of the Modbus Server device to associate with the trigger. The trigger will execute only when this specific Modbus Server device receives a write command.
Modbus Command	Select the Modbus write command that will execute the trigger: Any - The trigger will execute when the Modbus Server receives any of the Modbus write coil or write register commands. 0x05 Write Single Coil - The trigger will execute when the Modbus Server receives the 0x05 Write Single Coil command. 0x06 Write Single Register - The trigger will execute when the Modbus Server receives the the 0x06 Write Single Register command. 0x0F Write Multiple Coils - The trigger will execute when the Modbus Server receives the 0x0F Write Multiple Coils command. 0x10 Write Multiple Registers - The trigger will execute when the Modbus Server receives the 0x10 Write Multiple command.

Parameter

Description

Device Name

Select the name of the Modbus Server device to associate with the trigger. The trigger will execute only when this specific Modbus Server device receives a write command.

Modbus Command

Select the Modbus write command that will execute the trigger:

Any - The trigger will execute when the Modbus Server receives any of the Modbus write coil or write register commands.
0x05 Write Single Coil - The trigger will execute when the Modbus Server receives the 0x05 Write Single Coil command.
0x06 Write Single Register - The trigger will execute when the Modbus Server receives the the 0x06 Write Single Register command.
0x0F Write Multiple Coils - The trigger will execute when the Modbus Server receives the 0x0F Write Multiple Coils command.
0x10 Write Multiple Registers - The trigger will execute when the Modbus Server receives the 0x10 Write Multiple command.

Modbus Server Write event type trigger event variables

When the Modbus Server Write event type trigger executes, the Modbus write command information is available to the trigger as Input event variables. The trigger event variables available to trigger actions that have input or source parameters are:

Event Variable	Data type	Description
Command	UINT1	The Modbus write command that was received by the Modbus Server.
Count of Items Written	UINT4	The number of coils or registers that were written by the write command. This value will be 1 for the Write Single Coil and Write Single Register commands.
Data	Binary	The data that was written in the Modbus Server, as specified in the Modbus write command.
Device Name	String	The name of the Modbus Server device that was written to.
IP Address or Port	String	The address of the Modbus client that sent the Modus write command. This will be an IP Address if the client is connected to the server via an Ethernet (Modbus/TCP) connection. This will be the serial port for Modbus RTU clients.
Starting Address	UINT4	For command values of 0x05 or 0x0F, the array offset in the Coils array. For command values of 0x06 or 0x10, the array offset in the Holding Registers array. This value will be zero-based even if the Modbus Server Start Address setting is set to One