AVEVA™ Plant SCADA

MelsecQnA - Hardware Setup

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MelsecQnA - Hardware Setup

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Last UpdatedAug 04, 2025
4 minute read

MelsecQnA PLC Setup

Apart from 10BASE5 or 10BASE2 Ethernet cabling, no special hardware setup is required for a Plant SCADA interface.

The PLC has to be programmed to operate the AJ71QE71 interface. Following is an example of the ladder logic to enable the TCP/IP port to work. This example uses ports 1020 & 1021. This code needs to exist in the initethet section of the QNA code.

Note: MelsecQnA devices support an AutoUDP port (port 5001) that opens when a module is initialized with an IP address. Using this port for SCADA communications is not recommended, as other applications may attempt to access the same device via the AutoUDP port.

Plant SCADA Computer Setup

It is recommended that you setup your specific Ethernet card as required and confirm basic network communications before proceeding with the communications configuration for the MELSECQ driver. Refer to the documentation accompanying your hardware for instructions.

To set up the MelsecQ software

Open Mitsubishi GX Developer, and then double-click Network parameters to display the dialog box.
Click MELSECNET/Ethernet . The Ethernet Operations dialog box appears.
Enter the parameters in the module listbox.
Click Operational Settings .
Enter the IP address .
Click End.
Save and write data to the PLC.
Manually reboot the PLC to reset the program memory.
Choose Ethernet Diagnostics on the Diagnostics menu to check that IP address is correct. The Ethernet diagnosis dialog box should look like this:

Use the following screenshot of the Mitsubishi GX Developer to help you set up the PLC and Ethernet module. After entering your settings, the dialog boxes should look like this:

melsecnet1

AJ71QE71-B5, A1SJ71QE71-B2 and A1SJ71QE71-B5 Hardware

The B2 has a Coax cable connector for 10Base2 and the B5 has an AUI connector for 10Base5 type connections. Mitsubishi recommend using a Transceiver with SQETEST of HeartBeat functionality if using the B5 model.

Indicators on the front of the module

RUN	ON = Normal, OFF = Bad Thing (Normal Operation Display)
RDY	Flashing = On-Line and Good (Standard Display of communication exchange completion)
BSY	ON = Executing, OFF= Not Executing (Display during execution of communication exchange processing)
SW ERR	CPU error, CPU type error, or rotary switch error display ON = Error, OFF= Normal
COM ERR	ON = Communication Exchange Abnormality (Bad Thing)
CPU R/W	ON = Exchanging data with CPU
TRANS.S	ON = Data link command request executing
TRANS.R	ON = Data link RECV command request waiting
FTP	ON = FTP server function operating
B1 - B8	Communication line connection status ON = Open completed, OFF= Closed state
TEST	ON = Self diagnosis executing
TEST.ERR	ON = Error during self diagnosis

Operation Mode Switch

0	On-line
1	Off-line
2	Execute a self-diagnosis test using a self-loopback test
3	Execute a RAM test
4	Execute a ROM test
5	Execute am EEPROM test
6	F not used

Communication Exchange Condition Setting Switches

Recommended settings have been marked in blue. See also MelsecQnA - Hints and Tips for a summary of switch settings.

SW1	TCP Timeout error temporary circuit process selection. Selection of Circuit processing at the time of a transmission of a TCP time out error. OFF = Close the circuit ON = Do Not Close the Circuit For Plant SCADA keep it OFF
SW2	Data Code Selection Type of Data Communications supported: OFF= Binary Mode ON = ASCII Mode Mitsubishi has released a Windows version of their programming software that uses ASCII Mode for communicating with the Module. Plant SCADA normally uses Binary Mode, but there is also the ability to use the ASCII Mode.
SW3	Self start mode setting Selects the start mode when the QE71 is booted. OFF= Runs following Y19 (initial processing request signal) ON = Reads the parameters in the EEPROM buffer memory regardless of the Y19 (initial processing request signal) after power has been turned on or the module reset and then conducts initial processing of the contents. This switch should be OFF.
SW4 - SW6	Usage not possible (fixed to OFF).
SW7	CPU communications exchange timing setting Write Protect the PLC. OFF = Writing Prohibited ON = Writing allowed. If you want to write to the PLC then set this to ON.
SW8	Initial Timing Setting Select the Timing which starts Initial Processing. OFF= Quick Start (Start without Delay) when entirely constructed in a single network. OFF = Normal Start (start after a 20 sec delay) when entirely constructed in multiple networks. For Plant SCADA, keep it OFF.Select the Timing which starts Initial Processing. OFF= Quick Start (Start without Delay) when entirely constructed in a single network. OFF = Normal Start (start after a 20 sec delay) when entirely constructed in multiple networks. For Plant SCADA, keep it OFF.

AVEVA™ Plant SCADA