Schneider Optics Web Embedded Server - Manual (Page 92)

Quantum Ethernet TCP/IP Modbus Application Protocol
82 840 USE 115 00 Version 1.0
C.3 TCP/IP Specific Issues
C.3.1 Broadcast/Multicast
Although broadcast and/or multicast are supported by both IP network address and
IEEE 802.3 MAC address, the Modbus Application Protocol does not support either
broadcast or multicast at the application layer.
Schneider Automation’s Quantum PLCs use broadcast addressing because they
use ARP as the means of locating the destination node. The client interface to the
Modbus Application Protocol service on the PLC, the MSTR block, requires the
user to provide the destination IP address. Also the embedded stack does use a
pre-configured default gateway IP address in the case where ARP does not
succeed.
C.3.2 TCP Port Number
Schneider Automation has obtained a well-known system port from an Internet
Authority. Schneider Automation’s well-known system port number is 502. The
Internet Authority assigned the system port number 502 to asa-appl-proto with
Dennis Dubé as the company point of contact.
This port number allows Schneider Automation to transport various application
protocols over with TCP or UDP. The particular protocol is indicated by the value of
the proto_id parameter in the mbap_pdu. Currently the only assignment is 0
meaning Modbus Application Protocol.