Jump to content

Recommended Posts

Does anybody know if Vision controllers (ie V130) support Modbus TCP or do they support the Modbus RTU over TCP implementation. The difference is that the first follows the original Modbus TCP frames (ie no CRC) while the latter encapsulates the serial RTU framing sent over TCP media.

Which one is supported by Vision and the other Unitronics controllers?

Link to comment
Share on other sites

  • 2 weeks later...

Modbus RTU is not a TCP protocol.  Modbus TCP/IP is designed for sending over an Ethernet network (Vision optional) while Modbus RTU is designed to be sent over a serial network such as RS-485 (Vision standard).  It is common to confuse the data layer with the transport protocol.

Modbus TCP/IP = data layer; Ethernet = transport protocol.

Modbus RTU = data layer; RS-485 = transport protocol.

Modbus TCP/IP can be simplified as Modbus RTU with additional information in the data packet for sending over an Ethernet network.

Link to comment
Share on other sites

  • 3 weeks later...

I am afraid the answers above are still confusing. Malequardos asked if there is a support for Modbus TCP or for Modbus RTU over TCP. I think the correct answer is: The Vision controllers support Modbus TCP, not Modbus RTU over TCP.
Modbus TCP has its own specification by Schneider. Modbus RTU over TCP is what you get if you use serial / Ethernet converters for Modbus RTU communication. For better understanding, read e.g. this: http://www.simplymodbus.ca/TCP.htm

  • Upvote 1
Link to comment
Share on other sites

  • 2 years later...
  • MVP 2023

Look in the Visilogic Examples for Modbus on the PLC side.

This forum isn't about programming PC applications, but someone may speak up and help.  Your best bet for figuring out Modbus in python is your friend Dr. Google.  The PC will most probably be the Master, and the PLC will most probably be the Slave (or Server in today's politically correct IT-speak).

Like this-


Joe T.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...