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MELSEC-Q
7 DATA COMMUNICATIONS USING BIDIRECTIONAL PROTOCOL
7.2 Sending Data to the External Device
This section explains data transmission from the PLC CPU to the external device.
7.2.1 Transmission methods
The following shows the method of sending data to the external device through data
communication using the bidirectional protocol.
PLC CPU
PLC program
Buffer memory
Transmission area
Transmission
completed
1)
Write
(BIDOUT
instruction)
External
device
(00
H
to FF
H
)
4)
(When abnormal)
2)
(When normal)
(00
H
to FF
H
)
Any data
3)
5)
Data
Q series C24
Sum check code Data portion
Data length ENQ
ACK
NAK Error code
BIDOUT instruction
completion device
BIDOUT instruction
CH1/CH2 Control timing
Send instruction
Contents
BIDOUT
1) Data such as control data and transmission data are stored in the device designated
with the BIDOUT instruction and then the BIDOUT instruction is executed.
2) The transmission data count and transmission data are written into the
transmission area of the buffer memory.
3) The Q series C24 sends data by adding the control code ENQ at the beginning of
the data.
When "Sum check" is designated with GX Developer, the Q series C24 adds
the sum check code calculated by internal processing to the end of the
message and then transmits the message.
When "No sum check" is designated with GX Developer, no sum check code is
sent.
4) A response for the data transmission (for normal completion: ACK message; for
abnormal completion: NAK message) is received.
5) The execution of the BIDOUT instruction completes with the transmission
processing completion of the Q series C24.