Mitsubishi Melsec-L Series User Manual page 274

(2) When the receive process of the connected device is not supported
When the receive process of the connected device is not the one shown in (1), the following may occur when
"Enable TCP Maximum Segment Size Option transmission" is set for communications.
• When batch reading is executed from the connected device using the MC protocol, data cannot be
normally read.
• After replacing the E71 (which does not support the TCP Maximum Segment Size Option transmission
function) with the alternative module supporting the function, data cannot be normally read.
• Even though the value in Received TCP packet count (Address: 1B8
was changed, data cannot be received.
If these errors occur, select "Disable TCP Maximum Segment Size Option transmission".
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and 1B9 ) in the buffer memory
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