I have a small OEM style PLC with Modbus TCP support. VTSCADA easily reads data from the the controller. When "Enable Output" is checked however, there is no change in the PLC data table when "manual data" is entered.

A third party Modbus Simulator has no problem writing the data to the PLC.

VTS presents NO ERRORS on the Modbus Status.

Question,
The PLC Support folks say to use Modbus Command "06" or "16" (Single / Multiple word). How do I verify which command VTS is using? Any other suggestions would be appreciated.

Hey Ellifino,

You can learn more about identifying the Single/Word address structure in PLC's by reading up on our address suffixes in our help files linked here:https://www.trihedral.com/help/Content/D_Tags/Dev_DataSuffixesForTagIO.htm

Also, please check your PLC address to ensure it can be written to. You PLC may only allow analog writes in the 40XXX addresses, for example. Also, rather than using manual data, try drawing an input box widget and linking it to the address to see if you can update the value using that widget. The manual data is typically designed for testing and I'm not sure it is designed for writing values to a PLC. You can also try using an analog control tag to write a value to the PLC address as this tag type is designed specifically for this purpose which an analog status tag is designed primarily for monitoring.

Let us know if that helps.

Thank you for the feedback!! Using the Analog Input tag type did the trick. AND you are exactly right about drawing the Numeric Input object, the Manual Data still did not work, but as soon as i drew the object it worked perfectly.

Glad to hear it! Thanks for keeping us up-to-date on your progress.