Mitsubishi Electric Q26UD(E)HCPU User Manual page 293

Check item
The number of connections from the connected device
(personal computer) exceeds the number of "MELSOFT
connection" of the open setting (each number of connections
of TCP and UDP).
A device was powered off with the TCP/IP connection open.
Communication can be performed by increasing the value of
communication time check period or number of retries in the
detailed host station setting of "Transfer Setup".
Any of the following settings is incorrect on the CPU module
or connected device side.
• Network address
• Default router IP address
• Subnet mask pattern
• Router IP address
• Subnet mask
When a router is used, an error has occurred in the router.
When a router is used, the setting on the router is incorrect.
Any device on the network such as the CPU module,
connected device (personal computer), hub, or router is
replaced. (When replaced with the device of the same IP
address)
Communication is possible after replacement of the hub or
router.
If Ethernet communication cannot be performed even after taking the above actions, the possible cause is a
hardware failure.
Please consult your local Mitsubishi representative.
*1 If the switching hub is reconnected to the personal computer or CPU module or is replaced with another, it may take time
to read the MAC addresses. In that case, retry after a little while, or resupply power to the hub. If a dummy UDP
message is sent by the socket communication function, the switching hub may learn the MAC addresses again.
*2 Devices on the Ethernet have the "ARP cache", which is the correspondence table of the IP address and MAC address.
When a device on the network is replaced with the device of the same IP address, their MAC addresses stored in each
"ARP cache" become inconsistent, which may cause abnormal communication.
The "ARP cache" is updated by resetting the device or after a certain period of time. The time required for updating
differs depending on devices.
CHAPTER 15 TROUBLESHOOTING
Corrective action
Keep the number of connections of the connected device
(personal computer) within the number in the open setting.
The TCP/IP connection is left open.
Perform the following:
• Wait for about one minute, and retry after the connection is
closed by the alive check function of the CPU module.
• Increase the number of connections in the setting to
reserve a spare connection.
• Adjust the value of communication time check period or
number of retries.
• Check the condition of the cables, connected device
(personal computer), and CPU module.
Correct the setting.
Remove the error from the router.
Correct the setting on the router.
Reset the devices on the network.
The hub or router may be faulty.
Replace the hub or router.
*2
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