Mitsubishi Electric Q26UD(E)HCPU User Manual page 295

(5) Communication is slow or unstable
If communication is slow or unstable, check the following items.
Check item
IP addresses are duplicate.
The number of connections of UDP exceeds the number set
to "UDP" of the open setting (each number of connections of
MELSOFT connection and the MC protocol).
Communication is based on UDP.
Communication is not retried.
The hub, router, or cable has an error.
Communication of devices other than the CPU module is not
stable.
Many of unnecessary broadcast data are received.
(The broadcast data volume can be checked in "Connection
Status" in Ethernet diagnostics)
The Ethernet communication load of the CPU module is
high.
The interrupt program is used.
CHAPTER 15 TROUBLESHOOTING
Corrective action
Correct the duplicate IP address. The duplicate IP addresses
are checked in the following way.
• Detect the IP address using the Find CPU function.
• Remove the connected device from the network, and
perform PING with the IP address of the removed device.
If any device responds, IP addresses are duplicate.
Keep the number of connections of UDP within the number
of the open setting.
Perform communication on TCP.
Retry communication.
Increase the number of retries.
Replace the hub, router, or cable.
• Take noise reduction measures.
• Check the amount of network traffic. If the traffic causes
instability, reduce the amount of traffic.
To reduce the Ethernet communication load of the CPU
module, increase the service processing time in the service
processing setting of the PC parameter.
Reduce the broadcast data volume on the network.
• Identify a broadcasting device, and restrict the broadcast
data volume. (Devices such as personal computers or
routers.)
• Use filtering of broadcast data with a router to prevent the
CPU module from receiving them.
• Separate the network with frequent broadcasts from the
network of the CPU module.
• Increase the service processing time in the service
processing setting of the PLC parameter.
• Reduce the number of connected devices.
• Reduce the communication frequency per connection and
data volume.
Reduce the frequency and process time of the interrupt
program.
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