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12.2 Troubleshooting
12.2.29 When Ethernet communication with CPU module is slow or unstable
12
TROUBLESHOOTING
12.2.29 When Ethernet communication with CPU module is slow or unstable
The following flowchart is provided to help you when Ethernet communication with a CPU
module is slow or unstable.
Completed
(To next page)
Ethernet communication with the CPU module
is slow or unstable.
NO
YES
Use UDP in MELSOFT connection for the specified
number of modules or less.
NO
Consult your network administrator and correct the hub.
NO
YES
YES
Use TCP instead of UDP.
Improved?
Use TCP.
NO
YES
Retry or increase the number of
retries. Improved?
Use retries. *
2
NO
YES
Replace the hub, router or cables.
Stabilized?
Replace the faulty one with another.
NO
YES
YES
NO
NO
YES
Set unique IP addresses.
YES
NO
Does a duplicate IP
address exist? *
1
Is UDP in
MELSOFT connection
or MC protocol used for more the number
of modules set by the
parameter?
Is the hub
capable of flow control
(IEEE802.3x PAUSE)?
Is the flow control enabled?
(Consult your network administrator.)
Use a hub that is capable of flow control.
Enable the flow control.
Is Ethernet
communication stabilized?
Is Ethernet
communication stabilized?
Is Ethernet
communication stabilized?
*1: Checking methods:
With the Find CPU function of GX Developer, check the QnUDE(H)CPU for
IP address duplication.
Disconnect a suspected device from the network, and run PING test from
another device to its address. If a reply is returned, there is a device with
a duplicate IP address.
Check respective IP address settings.
Using retries may increase stability of Ethernet communication.
*2: If transmissions pass through a wireless LAN, some packets may be lost resulting
in unstable Ethernet communication.
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