Receiving Methods; Data Reception From The External Device - Mitsubishi QJ71C24/-R2 User Manual

7 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL

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
2)
Read request
3)
Read
(BIDIN
instructions)
Arbirary data
(00
H
Contents
Reception data read request signal
BIDIN instruction completion device
BIDIN instruction
7 - 2
Q series C24
Buffer memory
Receive area
(When normal)
to FF )
H
CH1/CH2
X3/XA
Arbitrary data
1)
ENQ Data length Data area Sum check code
(00 to FF )
(When abnormal)
H H
Ignored
Error code
Control Timing
BIDIN
MELSEC-Q
External
device
2)
NAK
4)
ACK
7 - 2
7