Mitsubishi MELSEC LJ71C24, User Manual

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15 TROUBLESHOOTING
15.3.14 Undecodable data are transmitted or received
Symptom Cause Corrective action MC
Bi
di
re
ct
io
na
l
N
on-
procedural
Predefined
• With a multidrop link,
two or more devices
transmitted data at the
same time.
• Connect the external devices and the 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 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 C24 and external device
transmission rates.
• With a multidrop link,
the terminating resistor
is not connected
correctly.
• Check if the terminating resistor (110 or
330 in the case of the 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 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.