Mitsubishi Electric MELSEC iQ-R Series User Manual page 143

Comment can be set in the "Properties" screen displayed by right-clicking the module in "List of devices" or
"Device map area" and selecting "Properties." The following can be performed depending on the selected
device.
• Changing the image
• Creating association with a file or application
Existence Confirmation
When this product has not communicated with an external device for a certain period of time while the connection is open, an
alive check message is sent from this device to the external device. Whether the external device is alive can be checked if the
device can respond to the message.
Item Protocol
*1
KeepAlive TCP/IP
UDP UDP/IP
Do not confirm existence TCP/IP, UDP/IP
*1 Sends a presence confirmation message 22 seconds after the last message is received from a target device, and checks if there is a
response from the target device. If there is no response, then presence confirmation messages are sent in 1 second intervals. If
responses cannot be confirmed after 8 seconds (30 seconds after the final message was received), then the target device will be
considered not present, and the connection will be disconnected.
*2 If the target device does not support the TCP KeepAlive function (response to KeepAlive ACK message), the connection will be
disconnected.
*3 If an Ethernet-equipped module receives a PING command echo request command, an echo response packet will be sent in response
automatically. (Even if the connection used for data communications with the target device is closed, this will send a response to the
received PING command.)
In TCP connections, if there is no ACK response of the TCP/IP protocol to the transmission from a target device, the
retransmission processing will be performed at the retransmission count and interval which are shown below. If there is no
ACK response of the TCP/IP protocol in 60 seconds after the last retransmission, the target device will be considered faulty
and the connection will be disconnected.
*1
• Retransmission count : 12 times
*2
: (The number of retransmissions  the number of retransmissions  RTO
• Retransmission interval
*1 After 30 seconds from the establishment of the connection, a destination device error is assumed and the connection is disconnected
even if the number of retransmissions does not reach 12 times.
*2 The maximum value of the retransmission time is 60 seconds.
*3 RTO (retransmission timeout) is a value that increases exponentially based on RTT (round-trip time).
Description
This method is used for a connection opened using TCP/IP. This product performs an alive check by
sending an alive check ACK message to the target device with which communications have not been
performed for a certain period of time and waiting to see whether the response is received.
The connection will be automatically closed when the open state is not continued.
This method is used for a connection opened using UDP/IP. This product performs an alive check by
sending the PING command (ICMP echo request/response function) to the target device with which
communications have not been performed for a certain period of time and waiting to see whether the
*3
response is received.
Alive check is not performed.
*2
*3
)  1024 (seconds)
13 MELSOFT CONNECTION FUNCTION
13.1 Connection Method
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