from the Does MODBUS/TCP support broadcast? department...
Does MODBUS/TCP support broadcast?
Communications systems and equipment. topic
Posted by Aditya Joshi on 20 December, 2005 - 12:56 am
Does MODBUS/TCP support broadcast?

Posted by RSW on 3 February, 2006 - 11:42 pm
Since TCP protocol requires a connection to be established between two locations before communications can commence, I would think that this is not possible. Maybe there is a Modbus/UDP mode that would allow broadcast.

Posted by Lynn A Linse on 5 March, 2006 - 7:54 pm
Sorry - this a few months old.

Since the Modbus/TCP spec demands use of TCP/IP, one could not formally use IP-based "broadcast" to or even a subnet broadcast as that would require use of UDP/IP. Some products allow using UDP/Ip to move Modbus/TCP formating.

However, the growing importance of Ethernet and IP-based networks in factories means using IP broadcast for "normal protocols" is frowned up and any professional in charge of a factory-floor network would NOT use such a product. Broadcasts load every device on the network, and can cause product "A" to affect/kill unrelated product "B". In other words, turning on a CNC machine could bring down a security camera, etc.

best regards - LynnL,

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