106
Exchanging Data with the CPU Unit Section 5-1
• Communications Error Flags
A Communications Error Flag turns ON if the applicable Slave Unit
cannot communicate with the Master Unit for any reason after the
Slave Unit has joined the network (i.e., if the Participation Flag is ON).
It turns OFF when the error is removed.
Therefore, in the ladder program, the applicable Slave Unit has
stopped participating when both the Participation Flag and the Com-
munications Error Flag are ON. Similarly, the applicable Slave Unit is
operating normally when the Participation Flag is ON and the Commu-
nications Error Flag is OFF.
Example: This example shows the executing I/O with the applicable
Slave Unit when the Participation Flag and Communications Error Flag
are combined and taken as a condition to confirm that operation is nor-
mal.
• The operation of the Participation Flags and Communications Error Flags
depends on the status of SW4 (REGS) on the DIP switch on the front of
the Master Unit.
• A bit is allocated for each node address. The 8 input nodes are allocated
after the 8 output nodes.
Note When there are both inputs and outputs (i.e., for I/O Slaves), flags
are allocated only for the input node.
SW (REGS) of DIP
switch on front of
Master Unit
Object of Participation or Communications Error Flag
OFF (Registration
Table Disabled)
All Slave Units
ON (Registration
Table enabled)
Registered Slave Units only. Participation Flags and Com-
munications Error Flags for unregistered Slave Units do
not operate.
Slave Unit A
Participation
Flag
Slave Unit A
Communications
Error Flag
A communications
error occurs at
Slave Unit A.
The Slave Unit stops
participating, but the
Participation Flag remains ON.
The cause of the communica-
tions error is removed. (Slave
Unit A is automatically restored
to the network.)
Not par-
ticipating
Partici-
pating
Participating
A B
a
a
Participation
Flag
Communica-
tions Error Flag
Normal operation
Allocated I/O address
Input processing from
applicable Slave Unit
Normal
operation
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