Mitsubishi Melsec-L Series User Manual page 327

Read command
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REMARKS
When data is communicated using the MC protocol, the ERR. LED may not be
turned on if the C24 sends an NAK message to the external device in response to
the command message.
Error codes corresponding to the error content when the NAK message is sent back
to the external device are stored in the following areas. (When communicating with
an A compatible 1C frame, the error codes differ from the transmission error code.)
When checking error codes transmitted by the CPU module, incorporate the
following program (in the case of the interface on the CH1 side).
Check the error codes and take corrective actions according to Section 15.2.
15 TROUBLESHOOTING
Reads transmission error codes from address 25A
Clears error codes.
.
H
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