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Checking Data Link Status Section 5-4
5. With CS/CJ-series PLCs, the status of the words from first status word +
16 to first status word + 30 when 8-bit format is specified and the status of
the words from first status word + 8 to first status word + 15 (i.e., the status
of nodes 33 to 62) is reflected when the Wired Network 62 Node Enable
Bit in the DM Parameter Area is turned ON.
The flags in the data link status operate as follows:
The Data Link Participation Flag and the PLC Status Flag can be used to see
if the system has started normally. These flags, however, cannot be used to
detect communications errors. Use the Communications Error Flag and PLC’s
CPU Unit Error Flag to detect errors.
If the Local Node Data Link Participation Flag is OFF, the previous status will
be maintained as the data link status and may not be correct. Make sure that
the Local Node Data Link Participation Flag is ON before checking data link
status.
Note The following Local Node Data Link Participation Flags are available.
CS/CJ-series, CVM1, CV-series PLCs:
Bit 15 in 1500 + 25
× unit number + 6
C200HX/HG/HE PLCs: SR 25205
CQM1H-series PLCs: IR 9015
Name Function
Data link participation The corresponding flag will turn ON if the node has never
participated in the data link normally. The flag will not turn
OFF once it has turned ON even if the node is no longer par-
ticipating in the data links.
Communications
error
The corresponding flag will turn ON if continuous data link
data cannot be received from the node, e.g., due to a cable
break. The flag will turn OFF again if normal data is received.
PLC’s CPU Unit error The corresponding flag will turn ON if the CPU Unit has a
fatal error, non-fatal error, or watchdog timer error. The flag
will turn OFF again if the node returns to normal.
The status of this flag is based on data sent from the node
and will not turn ON if data cannot received, e.g., due to a
Communications Error. Make sure that the Communications
Error Flag is OFF before checking this flag.
PLC status The corresponding flag will turn ON if the user program is
being executed in the CPU Unit. It will turn OFF is the user
program is not being executed.
The status of this flag is based on data sent from the node
and will not turn ON if data cannot received, e.g., due to a
Communications Error. Make sure that the Communications
Error Flag is OFF before checking this flag.