5DATA COMMUNICATION USING THE MELSEC COMMUNICATION PROTOCOL

MELSEC-Q

(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

5

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

Station No.

PC No.

Command

H L H L

 

0 0 0 1 Q R

waitMessage 0

No. of device

points

Head device 2 characters (hexadecimal)

H L

X 0

0

0

0

4

0

0

2

check

code

Sum

 

H

L

7

2

S T X

No.

No.

Data for the number

E

Station

PC

of device points

T

Number of device

X

 

 

points × 4 characters

H L H L

 

 

0 0 0 1 1 2 3 4 A B C D

check

code

Sum

 

H

L

9

8

05H 30H 30H 30H 31H 51H 52H 30H 58H 30H 30H 30H 30H 34H 30H 30H 32H 37H 32H

02H 30H 30H 30H 31H31H 32H 33H 34H 41H 42H 43H 44H 03H 39H 38H

(Command message for A compatible 1C frame)

(Response for A compatible 1C frame)

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.

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