Undecodable Data Are Transmitted Or Received - Mitsubishi QJ71C24N User Manual

11 TROUBLESHOOTING

11.3.14 Undecodable data are transmitted or received.

Symptom
• Data that cannot be
decoded was
transmitted and
received
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Cause
• With a multidrop link,
two or more devices
transmitted data at the
same time.
• Data does not match
the parity bit setting.
• Data does not match
the parity bit setting.
• Transmission rate
settings do not match.
• With a multidrop link,
the terminal resistor is
not connected
correctly.
• When CH1 and CH2
are used to the linked
mode, there is an
interface without cable
connection.
Corrective action
• 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.
• 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.
• Match the Q series C24 and external device
transmission rates.
• Check if the terminal resistor (110
330 in case of the Q series C24) is
connected to the stations at both ends of the
link.
• 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.
MELSEC-Q
or
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