Mitsubishi QJ71MB91 User Manual page 314

11
TROUBLESHOOTING
No. Symptom
Communication with the
target device is not
7 available even if
parameter setting has
been completed normally.
The interval of the
communications with the
slave in the automatic
communication function is
longer than the time set by
the automatic
8
communication
parameter, Request
interval timer value.
The time to complete the
dedicated instruction is
too long.
11
- 9 11.1 Troubleshooting
Table11.3 Troubleshooting for other symptoms (Continued)
Check point
Is the communication cable between the
QJ71MB91 and the target device securely
connected?
Is the communication cable wiring
correct?
Are the specifications of the
communication cable in use correct?
When both of 2-wire and 4-wire devices
are used with RS-422/485, is the wiring
correct?
Check the communication target device.
• Check for errors.
• Check if the device is ready for
operation.
• Check if it attempts to communicate with
the QJ71MB91.
Check for any other masters if the
QJ71MB91 is the master.
When the QJ71MB91 is the master, check
if the communication target device is a
MODBUS slave device.
When the QJ71MB91 is a slave, check if
the communication target device is a
MODBUS master device.
Check the communication target device.
• Check for errors.
• Check if the device is ready for
operation.
Check if some send requests by the
automatic communication function and
dedicated instruction were concurrently
issued on the QJ71MB91 side.
Check if it takes time for the target device
to respond.
Corrective action
Securely connect the communication
cable.
Check the specifications of the
communication cable used.
Confirm the specifications of the
communication cable used.
Check the specifications of each device,
and examine the wiring.
If a problem is identified on the
communication target device, take
corrective actions.
Only one master is allowed on the
MODBUS system. Disconnect the other
master.
Set a MODBUS slave device as the
communication target.
Set a MODBUS master device as the
communication target device.
If a problem is identified on the
communication target device, take
corrective actions.
• It takes time to send concurrently issued
requests as they are processed in
sequence.
Reduce the load on the QJ71MB91.
• Set appropriate automatic
communication parameters and create
a proper sequence program so that
each of dedicated instructions can be
executed in the right timing.
• Check the processing performance of
the communication target device.
• If a problem is identified on the
communication target device, take
corrective actions.
(Continued on next page)
Reference
Section 6.5
Section 3.2
Section 3.3
Section 3.2
Section 3.3
Section 6.5.2
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Section 9.2.3
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