Hardware Information Communication Error "Nak" Occurs; Communication Is Intermittent - Mitsubishi Electric MELSEC iQ-R Series User Manual

Hardware information communication error "NAK" occurs

Symptom Cause
Hardware information Refer to section which
communication error signal describes the communication
"NAK" turns ON. error signal ("C/N", "P/S",
"PRO", "SIO") that are turned
ON simultaneously when the
"NAK" signal is turned ON.
■Remarks
When the "NAK" signal is turned ON, the error code is added to "NAK" and is transmitted from
C24 to the target device. Take the corrective action depending on the error code listed below.
Page 473 Error Code List
In addition, the error code when "NAK" is transmitted is stored to the C24 buffer memory shown
below, so it can be checked at the C24 side as well.
• Error code storage buffer memory
CH1 side: Un\G602
CH2 side: Un\G618

Communication is intermittent

Symptom Cause
Communications are During multidrop connection,
intermittently established and two or more devices
lost. transmitted data at the same
time.
The signal cable wiring has a
loose connection.
The CD(DCD) signal turns
ON/OFF repeatedly when the
CD terminal check is enabled.
When half-duplex
communications is set, the
ON/OFF timing of each signal
does not match.
The next transmission
processing was requested
before a previous
transmission processing had
been completed.
The next reception
processing was requested
before a previous reception
processing had been
completed.
Communication via modem is
disrupted.
The data sent from C24 are
received back to the RS-422/
485 interface (CH2) side.
Corrective action
• Take corrective action corresponding to the contents of the
error.
Corrective action
• Connect the target devices to C24 on a 1:1 basis and
perform a loopback test.
If C24 can communicate normally with each of all target
devices, two or more devices transmit data simultaneously
during multidrop communication. Therefore, interlock the
devices not to transmit at the same time.
• Replace the cable, or make the connections firm.
• Change the wiring so that the CD(DCD) signal remains ON
all the time, or change the setting so that the CD terminal
check is disabled.
• Control at the target device side so that the ON/OFF timing
of each signal matches.
For details, refer to the following section.
(Page 243 DATA COMMUNICATIONS USING HALF-
DUPLEX COMMUNICATIONS)
• Make sure to obtain handshake in the program.
• Since communication via modem may be disrupted due to
low line quality or instantaneous interruption, create a
program for reconnecting the line in case of unexpected line
disruption.
• If this symptom occurs frequently, reduce the
communication rate of the modem, and retry the
communication.
• Disable the echo back with the Echo back enable/disable
designation before communication.
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27 TROUBLESHOOTING
27.3 Troubleshooting by Symptom
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