Modbus/TCP Driver Configuration - Advanced Settings

Timestamp mode

Defines the timestamp mode (with or without milliseconds) for float transformations.

Register Endianness

Defines which endianness should be used when reading or writing to a register.

Only active driver

This option defines that only the active driver connects to the PLC. You must use this option in a redundant WinCC OA system if the PLC only supports a single Modbus client connection.

Swapped Bytes

Defines whether the Modbus driver swaps the bytes of 16-bit Modbus registers (holding and input) for the connection.

Activate Address Offset

Defines whether an offset between Modbus address and device address is applied. Useful for devices that start internal addressing at 1, which corresponds to Modbus address 0.

Figure 1. Configuration panel of the Modbus/TCP driver (Advanced settings)

Alive Timeout Message

Configures a cyclic Modbus request used to check the connection to the PLC. A combobox selects the Modbus Function Code (FC) for the Alive Timeout Message. Supported values:

  • use default – Uses the global setting [mod] aliveTimeoutMsg.
  • read coils
  • read input discretes
  • read multiple registers
  • read input registers

With use default, the reference number field (Ref Nr.) is disabled. A numeric spin button defines the address used for the Alive Timeout Message (0–65535, unsigned 16 bit). Only enabled when the function code is not “use default”.

The datapoint _Mod_Plc.AliveTimeoutMsg of type When use default is selected, the reference number cannot be set. The reference number is only editable when another function code is chosen.

The datapoint _Mod_Plc.AliveTimeoutMsg of type >>>>>>> e31cf64 Added comment to PR uint stores the configuration in packed form:

  • High 16 bits: function code
  • Low 16 bits: reference number