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MELSEC-Q
10 DEVICES
10.2.8 Link special relays (SB)
(1) Definition
(a) A link special relay indicates the communication status and error detection
of an intelligent function module, such as the MELSECNET/H Network
Module.
(b) Because link special relays are switched ON and OFF in accordance with
various problems which may occur during a data link, they serve as a tool
for identifying data link problems.
(2) Number of link special relay points
There are a total of 2048 link special relay points between SB0 and SB7FF. Link
special relays are assigned at a rate of 512 points per each intelligent function
module, such as the MELSECNET/H Network Module. Link special relays are
assigned as shown below.
For 1st network module
For 2nd network module
For 3rd network module
For 4th network module
SB200
SB3FF
SB400
SB5FF
SB600
SB7FF
SB0
SB1FF
512 points
512 points
512 points
512 points
2048 points
REMARK
For details on link special relays used at the QCPU, refer to the QCPU (Q
mode)/QnACPU Programming Manual (Common Instructions).
10.2.9 Step relays (S)
A step relay is an SFC program device.
For details regarding procedures for using step relays, refer to the QCPU (Q
mode)/QnACPU Programming Manual (SFC).
POINT
Because the step relay is a device exclusively for the SFC program, it cannot be
used as an internal relay in the sequence program.
If used in this manner a SFC error will occur, and system operation will be stopped
(system down).
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