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MELSEC-Q
5 DATA COMMUNICATION USING THE MELSEC COMMUNICATION
PROTOCOL
5
(4) Monitoring the PLC CPU
This function monitors the operating status of the PLC CPU and the data in the
device memory.
The PLC CPU status and the device memory data can be sent to the external
device at fixed intervals, when an error occurs in the machine equipment, or
when certain conditions are satisfied.
This function reduces the data read processing load on the external device side.
(5) Sending data from the PLC CPU to the external device
A function for requesting data transmission from the PLC CPU to the external
device is called the on-demand function.
Urgent data that must be forwarded to the external device can be sent as on-
demand data to the external device by starting up from the PLC CPU.
5.1.2 Message format and control procedure for data communication
The data communication functions using the MC protocol correspond to the data
communication functions using the dedicated protocol for the conventional products
listed below.
• A series computer link module
• QnA series serial communication module
Therefore, the message format and control procedure are the same as when
accessing the PLC using these conventional modules.
The external device side can access the Q series PLC with a program used for
accessing the PLC via a conventional module.
(Example)
E
N
Q
HLHL H L H L
0001QR 0 X000040 0 2
2
7
05
H
30
H
30
H
30
H
31
H
51
H
52
H
30
H
58
H
30
H
30
H
30
H
30
H
34
H
30
H
30
H
32
H
37
H
32
H
S
T
X
HLHL
0001
1
234 BCD
02
H
30
H
30
H
30
H
31
H
31
H
32
H
33
H
34
H
42
H
43
H
44
H
HL
8
9
39
H
38
H
E
T
X
03
H
A
41
H
(Command message for A compatible 1C frame) (Response for A compatible 1C frame)
Station No.
PC No.
Command
Message wait
Head device
No. of device
points
2 characters
(hexadecimal)
Sum check
code
Sum check
code
Station No.
PC No.
Data for the number
of device points
Number of device
points × 4 characters
POINT
The following manual is available for performing data communication using the MC
protocol.
MELSEC Communication Protocol Reference Manual (sold separately)
5.1.3 PLC CPU setting for performing data communication
Data communication using the MC protocol is achieved by performing the GX
Developer settings indicated below on a PC, performing the system settings by the GX
Configurator-SC, and registering the settings to the PLC.
(1) Settings using the GX Developer (Required)
Perform the I/O assignments and switch settings indicated in Section 4.5 and
write the parameters to the PLC CPU where the Q series C24 is installed.