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MELSEC-Q
7 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
7
7.1 Data Reception from the External Device
This section explains the data reception from the external device.
7.1.1 Receiving methods
The following shows how to receive data sent from the external device using the
bidirectional protocol. Since the size of each message received is recognized using the
"data length" information contained in the message, messages of any size can be sent
from the external device.
PLC CPU
Sequence
program
3)
Read
(BIDIN
instructions)
External
device
1)
Arbirary data
(00
H
to FF
H
)
4)
2)
2)
Read request
(00
H
to FF
H
)
Buffer memory
Receive area
Q series C24
(When normal)
ENQ Data length Data area
Sum check code
Arbitrary data
(When abnormal)
Ignored
Error code NAK
ACK
Reception data read request signal
BIDIN instruction completion device
BIDIN instruction
CH1/CH2
X3/XA
Control Timing
BIDIN
Contents