Getting started

Start here

Use this page to make your first MELSEC SLMP read from Node-RED. Start with one simple TCP flow, then move to arrays, strings, UDP, routing, or broader verification.

Prerequisites

Requirement	Value
Node.js	18 or later
Node-RED	3.0 or later
PLC	MELSEC PLC reachable from your Node-RED host
First TCP target	192.168.250.100:1025
Starting PLC profile	melsec:iq-r

Install

1. Open the Node-RED editor.
2. Open Manage palette.
3. Open the Install tab.
4. Search for @fa_yoshinobu/node-red-contrib-plc-comm-slmp.
5. Install the package.
6. Restart Node-RED if your environment requires it.

Create a connection node

Create or open a slmp-connection config node and set these fields:

slmp-connection field	Example value	Description
Host	192.168.250.100	PLC IP address or host name.
Port	1025	TCP port for the first example.
Transport	TCP	Use TCP for the first run.
PLC profile	melsec:iq-r	Required canonical PLC profile.

Confirm all route fields initialized by the editor. Use the own-station values unless your PLC network needs a different target.

Import the basic flow

1. Open the Node-RED import dialog.
2. Import examples/flows/slmp-basic-read-write.json.
3. Open its slmp-connection node.
4. Confirm Host is 192.168.250.100.
5. Confirm Port is 1025.
6. Confirm Transport is TCP.
7. Confirm the PLC profile is melsec:iq-r.
8. Deploy.
9. Trigger the read inject node.
10. Open the debug sidebar and verify msg.payload.

The optional Test values (random + restore) Inject is state-changing. Use it only after replacing the sample addresses with controlled test addresses. It saves the original values, performs separate supported word and float writes, restores the snapshot after confirmed acknowledgements, and reads again. D302.3 remains read-only because it cannot be mixed into that named write contract. An error or outcome-unknown result stops the automatic sequence; inspect and reconcile the target values manually instead of retrying.

In object output mode, a successful read looks like this shape:

{
  "D300:U": 123
}

The value depends on your PLC memory.

Read your first value

To build the first read manually, add an slmp-read node and set:

slmp-read field	Example value	Description
Connection	Your slmp-connection node	Shared PLC connection.
Source	Literal text	The address list is entered in the editor.
Addresses	D300:U	First safe word register to read.
Output	Object payload	Returns an object keyed by address.
Metadata	Full msg.slmp	Includes connection and target metadata.
Errors	Throw	Lets Node-RED route runtime errors normally.

Trigger the node with any message. A successful response sets msg.payload["D300:U"] to the current value.

Confirm success

1. The flow deploys without editor validation errors.
2. The slmp-connection node has PLC profile melsec:iq-r.
3. The PLC-side communication data code is Binary and the port/open setting matches your transport; see the MELSEC SLMP PLC Setup Guide.
4. PLC-side RUN-time write permission is enabled before you run a write flow where the PLC exposes that setting, and every write address is a controlled test address.
5. The read inject node produces a debug message.
6. msg.payload contains a D300:U key.
7. The connection status does not stay red after repeated reads.

If it does not work

Symptom	Check
The read returns nothing or errors immediately	PLC profile on slmp-connection must be set. It is required, and there is no runtime default.
Connection opens but all requests fail	Confirm Binary communication data code in the PLC setup guide.
Reads work but writes fail	Confirm RUN-time write permission in the PLC setup guide and the selected profile write policy.
The first flow feels too busy	Import slmp-basic-read-write.json first, not slmp-device-matrix.json.
Address validation fails on the first run	Start with D300:U. Do not test with G or HG on the first run.
TCP does not connect	Confirm the PLC is reachable at 192.168.250.100:1025 from the Node-RED host.
UDP is your target	Move to the UDP example after TCP works, and set the UDP port to 1035.