I copied this info Direct from the MODBUS.ORG website: "Modbus TCP/IP simply takes the Modbus instruction set and wraps TCP/IP around it"

Wich raises a question; The MODBUS instruction set they mention, is that all 'flavors' of modbus (i.e. ENRON, standard,etc..)

Leading to.... Is it possible to communicate ENRON MODBUS via MODBUS TCP/IP and still gather the Archives, date/time, register data etc.?

I ask because we are currently communicating to our Bristol RTU's in the Field via satellite using serial comms from the earth station to the RTU. If we could convert to TCP/IP this would be a great advantage for future upgrades.

Does anyone have a clear understanding on this?

 

There are actually (at least) two ways to send modbus over TCP/IP.

Modbus "RTU over TCP" is like you stated. It's just the modbus RTU message with a TCP wrapper.

Modbus "TCP" also changes the message format. It replaces the one byte RTU address at the start of the message with a six byte MBAP header, as well as dropping the CRC from the end.

Both ways are capable of using the ENRON modifications for sending history archives, alarms and 32 bit registers.
This is better explained at www.simplymodbus.ca/TCP.htm

This site also has a good TCP test program that supports both methods with the ENRON 'flavor'.