Configure the Mitsubishi MELSEC Connector

Configure Mitsubishi MELSEC instances and items, discover PLCs, address MC protocol memory, read and write values, and troubleshoot communication.

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The Mitsubishi MELSEC Connector communicates with Mitsubishi PLCs through MC protocol or SLMP over TCP/IP. Use it to read and write supported PLC memory areas and to discover compatible PLCs on a local IPv4 network.

This guide explains how to configure an instance, discover PLCs, create items manually, select data types, address PLC memory, and resolve common communication errors.

The Connector supports TCP/IP connections only. Configure an MC protocol or SLMP TCP connection in the PLC before creating the instance.

Before you begin

Make sure that:

The PLC Ethernet interface has a known IPv4 address.
SIA Connect can reach the PLC network.
MC protocol or SLMP communication is enabled in the PLC project.
You know the configured TCP port, communication format, and PLC model or frame type.
You know the memory addresses and data types you want to use.
The PLC allows a TCP client connection from SIA Connect.

Some PLC ports allow only one TCP session. Disconnect GX Works or another active client when the PLC refuses a connection or cannot be identified during discovery.

Create a Mitsubishi MELSEC instance manually

In the Edge Portal, open Workspace > Instances.
Select Add instance.
Select the Mitsubishi MELSEC Connector.
Enter a descriptive instance name.
Enter the PLC IPv4 address in Address.
Select the communication Mode and Model.
Enter the PLC TCP Port.
Configure the timeout, device ID, and network ID.
Save the instance.

Instance parameters

Parameter	Required	Default	Description
Address	Yes	None	IPv4 address of the PLC. The instance validator requires an IPv4 address.
Timeout	Yes	`2000` ms	Connection and response timeout in milliseconds. Values below `10` ms are treated as `10` ms.
Mode	Yes	None specified	Select Binary or ASCII. The selection must match the communication format configured in the PLC.
Model	Yes	None specified	Select the PLC family or MC protocol frame profile that matches the target PLC and its Ethernet configuration.
Port	Yes	None	TCP port configured for MC protocol or SLMP communication. Use a port from `1025` to `65535`.
Device ID	Yes	`255`	Station number of the target device in a multidrop or routed network. Use `255` for a direct connection.
Network ID	Yes	`0`	Network number of the target device. Use `0` for a direct connection.

Model selections

The current Connector provides these model and frame selections:

Q series
Q series built-in ethernet
L series
iQ-R series
iQ-F series
FX series
SLMP
A series
3E frame (Multi block)
3E frame (Block)
3E frame (Multi block iQ-R subcommands)
1E frame

Select the PLC family when it is listed. Use a frame-specific option when the PLC or Ethernet module requires that MC protocol frame format. If the PLC rejects commands, confirm the frame type in the Mitsubishi configuration software and device manual.

Discover Mitsubishi MELSEC instances

The Connector can discover PLCs on a local IPv4 subnet. It first sends MELSOFT and SLMP broadcast searches on UDP ports 5006 and 5000. It then checks the configured TCP ports to identify an MC protocol or SLMP connection.

Open Configuration > Connectors.
Find the installed and enabled Mitsubishi MELSEC Connector.
Disable an existing instance that is already connected to the PLC when the PLC permits only one TCP session.
Select Discover instances.
Configure the discovery parameters.
Select Search instances.
Wait for the search to finish.
Select the required PLC candidates.
Import the selected instances.
Open each imported instance and verify its model and connection settings.

Discovery fills the PLC address, detected TCP port, Binary mode, Device ID 255, Network ID 0, and a model based on the returned CPU information when possible. If the CPU type cannot be mapped, the imported instance uses Q series. Always verify the model before enabling the instance.

Discovery parameters

Parameter	Default	Accepted values	Description
Scan duration (ms)	`60000`	`1000` to `300000`	Maximum overall discovery window in milliseconds. The Connector uses part of this time for UDP discovery and the remaining time for TCP subnet probing.
Network interface	`eth0`	An available IPv4 interface or All IPv4 interfaces	Interface used for broadcast discovery and TCP subnet scanning.
TCP ports	`4998-5002, 5007, 5010, 6000`	Comma-separated ports and ranges from `1025` to `65535`	Ports checked for MC protocol or SLMP. For example, `4998-5002,5007`. The Connector scans up to 64 ports.

The TCP subnet scan checks up to 256 hosts. A PLC outside the local subnet, using a custom port not included in the list, or blocked by a firewall may not appear. Create the instance manually when discovery cannot reach it.

The Connector supports instance discovery only. MC protocol and SLMP do not provide tag browsing, so Discover items is not available. Create each data item manually.

Create an item

Open the Mitsubishi MELSEC instance.
Open the Items section.
Select Add item.
Enter a descriptive item name.
Enter the PLC address in Memory address.
Select the matching Data type.
Save and enable the item.

The Connector removes spaces and tab characters from memory addresses and treats device-code letters without regard to case. The prefix DM is accepted as an alias for D.

Item parameters

Parameter	Required	Description
Memory address	Yes	MC protocol device code followed by the memory location. Examples include `D100`, `M20`, and `W100.3`.
Data type	Yes	Format used to determine how many PLC words to read or write and how the value is converted.

Data types

Data type	Size	Example	Description
BIT	1 bit or selected bit in a word	`M20` or `D100.3`	Boolean value returned as `0` or `1`.
Short	1 word	`D100`	Signed 16-bit integer.
Long	2 words	`D100`	Signed 32-bit integer.
LongLong	4 words	`D100`	Signed 64-bit integer.
Word	1 word	`D100`	Unsigned 16-bit integer.
DWord	2 words	`D100`	Unsigned 32-bit integer.
QWord	4 words	`D100`	Unsigned 64-bit integer.
BCD	1 word	`D100`	16-bit binary-coded decimal value.
LBCD	2 words	`D100`	32-bit binary-coded decimal value.
LLBCD	4 words	`D100`	64-bit binary-coded decimal value.
Float	2 words	`D100`	32-bit IEEE 754 floating-point value.
Double	4 words	`D100`	64-bit IEEE 754 floating-point value.
Word [Unsigned]/Bit String [16-bit]	1 word	`D100`	Raw 16-bit word represented as a hexadecimal string.
ASCII	1 word	`D100`	Two-byte character data stored in one PLC word.
String	Configured address range	`D100-119`	Text stored across an inclusive range of PLC words. The example uses 20 words.

Address individual bits

Use a bit device directly, such as M20, with the BIT data type.

To access one bit in a word device, append a decimal bit number from 0 to 15:

D100.3

A dotted address can only use the BIT data type. When writing a bit inside a word, the Connector first reads the complete word, changes the selected bit, and writes the updated word back to the PLC.

A read-modify-write operation can conflict with another controller or application changing the same word at the same time. Use a dedicated bit device when possible.

Supported memory device codes

The available address range depends on the selected PLC model and its configuration.

Memory type	Supported device codes	Number format
Bit devices	`SM`, `X`, `Y`, `M`, `L`, `F`, `V`, `B`, `TS`, `TC`, `LTS`, `LTC`, `STS`, `STC`, `LSTS`, `LSTC`, `CS`, `CC`, `LCS`, `LCC`, `SB`, `DX`, `DY`	Model-dependent. `X`, `Y`, `B`, `SB`, `DX`, and `DY` use hexadecimal device numbering in MC protocol.
Word devices	`SD`, `D`, `W`, `TN`, `STN`, `CN`, `SW`, `Z`, `R`, `ZR`, `RD`	Model-dependent. `W`, `SW`, and `ZR` use hexadecimal device numbering in MC protocol.
Double-word devices	`LTN`, `LSTN`, `LCN`, `LZ`	Decimal device numbering.

The selected model determines which device codes and frame encodings are available. A code listed here can still be unavailable on a particular PLC.

Automatic identity items

The Connector adds these read-only identity items to each instance:

Item	Description
Vendor	Reports Mitsubishi.
Model	Reports the CPU type name when the PLC responds to the model request. Model detection is attempted in Binary mode.

The Model value can remain empty when the selected PLC or frame profile does not support the CPU model request.

Verify the setup

Enable the Mitsubishi MELSEC instance.
Confirm that the instance does not report a connection or PLC response error.
Enable an item with a known memory address and data type.
Confirm that the item receives the expected value.
If the item is writable, perform a controlled write and verify the value in the PLC.
Restore the original value after testing when required.

Only test writes when changing the target memory value is safe for the connected process and equipment.

Troubleshoot the Mitsubishi MELSEC Connector

Message or symptom	Likely cause	Action
Invalid port or IP	The instance address is not a valid IPv4 address or the port is not numeric.	Enter the PLC IPv4 address and the configured MC protocol TCP port. Do not enter a URL or protocol prefix.
Timeout (<value>ms)	The PLC did not accept the connection or return a response before the timeout.	Check the address, port, cable, VLAN, routing, and firewall. Confirm that the PLC connection is enabled and increase the instance timeout when the network or PLC responds slowly.
Connection established, but the remote device closed the connection. Check the PLC communication settings and MC protocol parameters.	The TCP port is open, but the PLC rejected the session or request format.	Check the selected Mode, Model, TCP protocol setting, and MC protocol frame configuration. Confirm that another client is not occupying a single-session port.
Mode mismatch. Select ASCII or Mode mismatch. Select binary	The instance communication format does not match the PLC.	Change Mode to the format configured for the PLC connection.
Select A or FX or 1E model	The PLC returned a 1E frame response while another model profile was selected.	Select A series, FX series, or 1E frame as appropriate for the PLC.
Device id incorrect, Device or network id incorrect, or Network id incorrect	The access route in the request does not match the PLC or routed network.	For a direct connection, use Device ID `255` and Network ID `0`. For a routed connection, enter the station and network values configured in the PLC system.
invalid address or Device code/head incorrect	The memory address is incomplete, unsupported, or outside the addressing rules for the selected model.	Check the device code and memory number. Confirm that the memory area exists on the PLC and that the selected model supports it.
dataType not boolean	A dotted bit address is configured with a data type other than BIT.	Select BIT, or remove the bit suffix and read the complete word.
invalid data provided	A write value cannot be converted to the selected data type.	Enter a value within the valid range for the selected type. Use `0` or `1` for BIT.
Memory points and data length mismatch or data length invalid	The requested point count and selected data size do not match.	Check the data type and memory address. For String, confirm that the start and end addresses form a valid inclusive range.
The request cannot be executed to the CPU module.	The CPU does not allow the requested operation in its current state or configuration.	Check CPU access permissions, operating state, communication settings, and whether the selected command is supported.
Command/subcommand are specified incorrectly or the CPU does not support the command/subcommand	The selected model profile generated a command that the PLC does not support.	Select the correct PLC model or frame profile and confirm which MC protocol commands the CPU supports.
ASCII code data that cannot be converted to binary code was received from an external device.	The PLC received invalid ASCII frame content or the connection format is incorrect.	Confirm that both the PLC and Connector use ASCII mode. Check for another application sending incompatible data to the same port.
Poor communication between the Ethernet adapter and the PLC	The PLC reports an internal communication problem between its Ethernet interface and CPU.	Check the PLC hardware, module status, project settings, and internal module diagnostics.
Unsupported frame by SIA Connect, Unknown PLC response, or MC protocol error 0x...	The PLC returned a frame or error code that the Connector does not map to a specific message.	Record the error code, check the PLC diagnostics and Mitsubishi MC protocol documentation, then review the Connector logs.
Discovery finds no PLCs	The wrong interface or ports are selected, broadcast traffic is blocked, the PLC is outside the subnet, or its only TCP session is occupied.	Select the PLC-facing interface, include the configured TCP port, allow local UDP broadcast and TCP traffic, and disconnect other clients. Add the instance manually when the PLC is routed.
Discovery imports the wrong model	The CPU name was not returned or could not be mapped to a model profile.	Edit the imported instance and select the model or frame profile that matches the PLC configuration.
Read values are incorrect	The selected data type, memory address, model, or communication mode does not match the PLC data.	Confirm the address in GX Works, check the selected data type and word size, and verify the PLC model and Binary or ASCII setting.
A write changes the wrong part of a word	The dotted bit index is incorrect or another application changed the word during the read-modify-write sequence.	Check the bit number from `0` to `15`. Use a dedicated bit device when simultaneous word updates are possible.

Review the instance error, item error, PLC diagnostics, and SIA Connect system logs together. PLC response errors usually indicate the exact access route, command, address, or data setting that must be corrected.

mitsubishi melsec mc protocol slmp connector instances items discovery troubleshooting

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