Mitsubishi Electric MELSEC iQ-R Series User Manual page 320

(0) Set the request number and destination IP address for UCMM message communications, and start EtherNet/IP communications.
(13) By turning on M100, "M+RJ71GN11_SE_EIP_UCMMOriginator_MessageSend" is executed and the request data is sent to the server side.
When M120 is on, the response result from the server side is stored in D2000 or later. (Half of the response data size stored in D3005 (bytes) are stored
(rounded up).)
If the response data size is an odd number, only the lower 1 byte of the end device is stored.
Ensure that the request number to be set is not the same as the connection number used for Class3
communications or the request number used for other UCMM communications.
13 PROGRAMMING
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13.3 UCMM Message Communications Communication Example