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DeltaV Integration with Wago 750 Using Modbus TCP/IP
By Martin Berutti
Product: IOD-4101 - Modbus TCP/IP Master Driver (General Modbus TCP/IP Communications)

DeltaV Diagnostics view showing port statistics.This technical note describes the integration of Wago 750-841 IO to DeltaV using Modbus TCP/IP and the Virtual IO Module.

The purpose of this application note is to document the testing of a Modbus TCP/IP device, Wago 750-851 Controller and IO, with the DeltaV Virtual IO Module and the Modbus TCP/IP Driver. The testing was completed in MYNAH Technologies testing lab in Chesterfield, MO, USA. The following was tested and documented:

  • Third Party Device configuration and setup
  • Virtual IO Module configuration and setup
  • DeltaV configuration and setup
  • DeltaV control performance testing and performance indicators noted
  • Testing notes, observations, and comments
Testing system layout and architecture.

Third Party Device Configuration and Setup

Device Tested: Wago 750-841 Ethernet TCP/IP Programmable Fieldbus Controller.

The unit was shipped to MYNAH from the Wago headquarters in Germantown, WI. The test unit was pre-wired and assembled and included the following components:

  • Model 787-602 Power Supply
  • Model 750-841 Ethernet TCP/IP Programmable Fieldbus Controller
  • Model 750-402 4 Channel DI Module
  • Model 750-504 4 Channel DO Module
  • Model 750-467 2 Channel AI Module
  • Model 750-550 2 Channel AI Module
  • Model 750-600 End Module
Wago 750-841 Controller and IO

The 750-841 controller was configured using the Wago Ethernet Settings Utility v3.00.03. The unit was set up for default Modbus TCP/IP communications with Ethernet/IP communications disabled. A configuration summary is as follows:

Firmware Rev 01.11.01(09)
MAC Address 003DE00958F
IP Address
Subnet Mask

Per the user manual, the IO data for the 750-841 is represented in a process image table. Inputs are written to the input table with a starting address of 0, and can be read by the Modbus master as input registers. Outputs are read from the output table with a starting address of 512 and can be written by the Modbus master as holding registers.. Analog values are written to the first registers in the order of their placement in the IO rack, and discretes are written to the same registers following all AI values. Changing the location of the IO modules will change the placement of field values in the process image table.

Virtual IO Module Configuration and Setup

The DeltaV Virtual IO Module was configured with MYNAH Technologies’ VIMNET Explorer, v6.0.0.2. A configuration summary is as follows:

Driver Modbus TCP - Simplex
Firmware Rev 3.4.0
MAC Address 000EC1007088
IP Address
Subnet Mask

In the VIMNet Explorer application, the 750-841 controller was setup as device DEV01, using RTU TCP (port 502) communications and a Modbus address of 1.

Configuration of the communications in the VIMNet Explorer.

DeltaV Configuration and Setup

DeltaV v7.3 build 4069 was used for the testing. A new controller was commissioned, the Virtual IO Module was sensed as Prgrammable Serial Modules slots 57-60, and PO1 of card 57 was enabled. One device (for the 750-841 controller) and two datasets (input dataset and output dataset) were configured. A summary of the device and dataset communication is as follows:

Device Address 1
DS01 data direction Input
DS01 DeltaV Data Type 16 bit uint w/ status
DS01 Device Data Type 2
DS01 Data start address 0
DS01 Number of values 10
DS0 data direction Output
DS02 DeltaV Data Type 16 bit uint w/ status
DS02 Devise Data Type 3
DS02 Data start address 512
DS02 Number of values 10
DeltaV Explorer showing the “virtual” serial card configuration.

A DeltaV Module was built called WAGO_TEST for displaying the input and output registers from the 750-841 controller and for testing purposes. Analog IO values were displayed as unscaled 16 bit registers. Discrete IO values were displayed as individual bits after being extracted from the register using the BFI and BFO function blocks. A CALC block was used to cycle the output signals to the DO in the field upon each scan for tieback testing. The module was run at 100 msec for tieback performance testing.

DeltaV Module used for data display and tieback testing.

DeltaV Performance Testing

Tieback testing of DIO performance was run using the module described above. Analog IO was tested for continuity only and not for tieback speed. All output channels were hardwired at the IO card to the corresponding input. As stated before, the test module was given an execution time of 100 msec. The tests were run for 15 sec burst loads with all Discrete outputs cycled every module scan. Approximately 1000 data events were analyzed to determine the statistics below. Changes to the discrete output channels and the discrete input channels after the Boolean fans were logged into the DeltaV event journal. A summary of the testing results and DeltaV performance indicators is as follows:

DeltaV Module Execution Time 100 msec
Avg Discrete Tieback time 100 msec
Max Discrete Tieback Time 101 msec
Min Discrete Tieback Time 99 msec
Serial Port Max Scan Time 10 msec
Serial Port Avg Scan Time 4-7 msec
MD Controller Free Processor Time 100 MD
MD Controller Free Memory 15661088

Performance Summary and Other Observations:

  • Per Wago documentation, the 750-504 Discrete Output module has a maximum switching frequency of 1 kHz and the 750-402 Discrete Input module has an input filter of 3 msec. We saw no measurable lag at DeltaV that would include these values or the port scan rate. In general, the DeltaV tieback ran as fast as possible with current DeltaV execution cycles. Differences in the Min and Max tieback time should be attributed to precision errors.
  • This was a small test (only one IO block with four IO cards). DeltaV controller loading and port scan time will increase as more IO is added to the application. In general, each Modbus TCP/IP slave (IO block) will add 10 msec to the port scan time.
  • When testing the Analog IO we found an offset in the value displayed on the input register versus the value entered into the output register. Upon investigation, we found that the value is represented with 12 bit resolution on bit B3 to B14. B0 to B2 represent status information. Using this data in DeltaV will require scaling. For example an output of 0-100% will need to be converted to 0-4095 and multiplied by 8 before being written to the register. Inputs register will need to be divided by 8 and scaled from 0-4095 to get to 0-100%. To get status information the expression “R1.CV & 7” (for register R1) will need to be evaluated.
DeltaV Diagnostics view showing port statistics.


In summary, we found no problems in using the Wago 750-841 Ethernet TCP/IP Programmable Fieldbus Controller with DeltaV and the Virtual IO Module. Communication speed and performance was as expected and we had no problems with the device in setup or testing.