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MELSEC-Q
10 TROUBLESHOOTING
10.3.12 Troubleshooting when data that cannot be decoded is transmitted and received
Symptom Cause Corrective action MC
Bidirectional
Non
procedure
• With a multidrop link,
two or more devices
transmitted data at the
same time.
• Connect the external devices and the Q series
C24 in a 1:1 configuration and perform a
communications test.
Since data is transmitted simultaneously from
two or more devices with a multidrop link when
normal data communications among all the
devices is possible, interlock the external devices
so that they do not transmit simultaneously.
• Data does not match the
parity bit setting.
• Data does not match the
parity bit setting.
• Match the Q series C24 and external device
parity bit settings.
Note
• If the setting of one side is data bit length 7
bits and with parity and the setting of the
other side is data length 8 bits and without
parity, the number of transmission/receive
bits will be the same and the data will sent
and receive without generating an error.
• Transmission rate
settings do not match.
• Match the Q series C24 and external device
transmission rates.
• With a multidrop link, the
terminal resistor is not
connected correctly.
• Check if the terminal resistor (110
or 330
in case of the Q series C24) is connected to the
stations at both ends of the link.
• Data that cannot be
decoded was
transmitted and
received
• When CH1 and CH2 are
used to the linked mode,
there is an interface
without cable
connection.
• When using CH1 and CH2 independently,
check that the Q series C24 is not in the linked
mode.
• When using CH1 and CH2 in the linked mode,
also connect the cable to both of the interfaces.
Note
• If the cable is not connected to one of the
interfaces when CH1 and CH2 are used in
the linked mode, noise may enter and destroy
the data and "Data cannot be decoded" or
"Communication error cause" may occur.