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MELSEC-Q
6 DATA COMMUNICATION USING THE NON PROCEDURE PROTOCOL
6.3 Data Communications Precautions
The following describes the precautions to be taken during non procedure protocol
data communications.
(1) The Q series C24 transmission sequence initialization conditions
The initial status indicates the status where transmission has stopped and
reception data has been discarded.
The Q series C24 transmission sequence initialization conditions are as follows.
1) When the power is turned on, the Reset switch on the CPU panel is
operated, or the Q series C24 mode is switched
2) When the receive data was cleared.
3) When the CD signal was turned off when data communications were
performed by setting CD terminal check enable during full-duplex
communications through the RS-232 interface.
(2) Generation of framing error in external device
When nothing is transmitted from the Q series C24 to the external device through
the RS-422 or RS-422/485 interface, a framing error may be generated by the
noise etc, in the external device.
Send an arbitrary code to identify the head of the send data from the Q series
C24 to the external device.
Before data communication check the Q series C24 interface specifications.
(3) Data communications with external device (computer, etc.) over a
multidrop link
When the external device PLC CPU are connected by a 1:n multidrop link, each
the Q series C24 receives the data transmitted by the external device.
With a multidrop link, receive data by user frame (
1).
If data is not received by user frame, a sequence program that ignores the
receive data other than the receive data addressed to the local station by
sequence program, including the data indicating the objective PLC CPU in the
message, must be written.
(Sample message)
STX Space
Station
No. 0
CR LF
(02
H
)(20
H
)(32
H
)(32
H
)(0D
H
)(0A
H
)
(Example)
Station
No. 2
Data length
(BIN data)
Data
1 See chapter 11 of User's Manual (Application)