[LinuxPLC] Modbus/TCP Object Messaging


Thread Starter

Lynn Linse

I found the spec for the "MODBUS/TCP Object Messaging Protocol Extensions" which is designed to support data objects much like DeviceNet or Foundation Fieldbus does. The full spec is at

In a nutshell, they provide a new function (decimal 91) which indicates an object request follows. An object consists of some flags, Object Class Id, Instance Id, Service Code (like get attribute etc) and data based on the service code.

Technically it was created to allow SemaTech objects to be managed in Modbus PLC. It would be interesting to see if this has application in our LinuxPLC. We could do simple things like timers or complex things like the "AC/DC motor", "position controller" or "analog group" objects of

While this adds a bit of data complexity, Modbus/TCP is still stateless (no sessions to register or negotiate) so the implementation is orders of magnitude easier than full blown ControlNet or Foundation Fieldbus or DeviceNet.


Lynn August Linse, Senior Product Application Engineer
15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618
[email protected] www.lantronix.com
Tel: (949)450-7272 Fax: (949)453-7132

LinuxPLC mailing list
[email protected]