Usage guide

Available nodes

Node	Purpose
`slmp-connection`	Shared MELSEC SLMP connection profile for `slmp-read` and `slmp-write`.
`slmp-read`	Reads one or more device addresses and writes the result to `msg.payload`.
`slmp-write`	Writes one or more device values from static configuration or incoming messages.

slmp-connection config node

Config field	Description
Name	Optional label shown in the Node-RED editor.
Host	PLC host name or IP address. For the examples, use `192.168.250.100`.
Port	TCP or UDP port. Use `1025` for TCP examples and `1035` for UDP examples.
Transport	`tcp` or `udp`.
Timeout ms	Communication timeout in milliseconds.
PLC profile	Required canonical PLC profile. The current editor options are `melsec:iq-f`, `melsec:iq-r`, `melsec:iq-l`, `melsec:mx-f`, `melsec:mx-r`, `melsec:qcpu`, `melsec:lcpu`, `melsec:qnu`, and `melsec:qnudv`.
Remote password	Optional SLMP remote password credential. When set, the connection unlocks after opening and tries to lock before disconnecting.
Monitor timer	SLMP monitoring timer value sent in requests.
Network	Target network number, `0` to `255`.
Station	Target station number, `0` to `255`.
Module I/O	Target module I/O number, entered as hexadecimal such as `03FF`.
Multidrop	Target multidrop station number, `0` to `255`.

slmp-read node

Config field	Description
Name	Optional label shown in the editor.
Connection	The `slmp-connection` config node to use.
Source	Where to read the address list from: literal text, `msg`, `flow`, `global`, or `env`.
Addresses	Literal address list when Source is literal text. Use one address per line for clarity.
Route	Optional per-request route source: literal JSON, `msg`, `flow`, `global`, or `env`.
Route JSON	Literal route object with `network`, `station`, `moduleIO`, and `multidrop`.
Output	`object`, `array`, or `value` when exactly one address is requested.
Metadata	`full`, `minimal`, or `off` for `msg.slmp` output.
Errors	Throw, attach to `msg.error`, or send the failed message to a second output.

Msg field	Description
`msg.addresses`	Runtime address list. A string or array here takes priority over the configured Source.
`msg.payload`	Runtime address list when it is a string or array and `msg.addresses` is not set.
`msg.target`	Per-request route override object.
`msg.slmp.target`	Per-request route override when `msg.target` is not set.
`msg.topic`	`connect`, `disconnect`, or `reinitialize` controls the shared connection instead of reading.
`msg.connect`	When `true`, opens the shared connection.
`msg.disconnect`	When `true`, closes the shared connection.
`msg.reinitialize`	When `true`, closes and reconnects the shared connection.
`msg.slmpSkipUnsupported`	When `true`, unsupported-device errors become skipped messages instead of failures.
`msg.slmp.skipUnsupported`	Same skip flag inside `msg.slmp`.

Output field	Description
`msg.payload`	Read result. Object mode is keyed by normalized address, array mode follows address order, and value mode returns a scalar for one address.
`msg.slmp.addresses`	Full metadata mode only: normalized address list.
`msg.slmp.connection`	Full metadata mode only: effective connection profile, frame type, target, and remote password status.
`msg.slmp.target`	Full and minimal metadata modes: effective route target.
`msg.slmp.itemCount`	Minimal metadata mode only: number of requested addresses.
`msg.error`	Error object when Errors is `msg.error`, or on the second output when Errors is second output.

slmp-write node

Config field	Description
Name	Optional label shown in the editor.
Connection	The `slmp-connection` config node to use.
Source	Where to read updates from: literal text, `msg`, `flow`, `global`, or `env`.
Static updates	Literal JSON object or `address=value` lines when Source is literal text.
Route	Optional per-request route source: literal JSON, `msg`, `flow`, `global`, or `env`.
Route JSON	Literal route object with `network`, `station`, `moduleIO`, and `multidrop`.
Metadata	`full`, `minimal`, or `off` for `msg.slmp` output.
Errors	Throw, attach to `msg.error`, or send the failed message to a second output.

Msg field	Description
`msg.updates`	Runtime update object, for example `{ "D300": 123, "M1000": true }`.
`msg.payload`	Runtime update object or configured-source data when `msg.updates` is not set.
`msg.address`	Single-address write path.
`msg.dtype`	Optional data type for `msg.address` when the address has no suffix.
`msg.value`	Single-address write value. If omitted, `msg.payload` is used.
`msg.target`	Per-request route override object.
`msg.slmp.target`	Per-request route override when `msg.target` is not set.
`msg.topic`	`connect`, `disconnect`, or `reinitialize` controls the shared connection instead of writing.
`msg.connect`	When `true`, opens the shared connection.
`msg.disconnect`	When `true`, closes the shared connection.
`msg.reinitialize`	When `true`, closes and reconnects the shared connection.
`msg.slmpSkipUnsupported`	When `true`, unsupported-device errors become skipped messages instead of failures.
`msg.slmp.skipUnsupported`	Same skip flag inside `msg.slmp`.

Output field	Description
`msg.payload`	The incoming payload is preserved unless your flow changes it before the write.
`msg.slmp.updates`	Full metadata mode only: normalized update object.
`msg.slmp.connection`	Full metadata mode only: effective connection profile, frame type, target, and remote password status.
`msg.slmp.target`	Full and minimal metadata modes: effective route target.
`msg.slmp.itemCount`	Minimal metadata mode only: number of update addresses.
`msg.error`	Error object when Errors is `msg.error`, or on the second output when Errors is second output.

Address syntax

Form	Example	Meaning
Plain word	`D100`	Unsigned 16-bit word.
Signed word	`D100:S`	Signed 16-bit word.
Signed word alias	`D100:I`	Alias that normalizes to `D100:S`.
Unsigned dword	`D100:D`	Unsigned 32-bit value.
Signed dword	`D100:L`	Signed 32-bit value.
Float	`D100:F`	32-bit float.
String	`D100:STR,10`	UTF-8 string with a 10-byte maximum, packed two bytes per word.
String alias	`DSTR100,10`	Compatibility alias for `D100:STR,10`.
Bit in word	`D50.3`	One bit inside a word device.
Direct bit	`M1000`	One bit device.
Counted bit	`M1000,8`	Eight consecutive bit devices.
Counted word	`D100,4`	Four consecutive word values.

Long device families

Use explicit 32-bit forms for long current-value families:

Family	Use
`LTN`	`LTN0:D` or `LTN0:L`
`LSTN`	`LSTN0:D` or `LSTN0:L`
`LCN`	`LCN0:D` or `LCN0:L`
`LZ`	`LZ0:D` or `LZ0:L`

These are 32-bit families. Do not use direct plain word access for them; the lower-level direct word commands reject that shape. The explicit suffix also makes your flow portable and readable.

Connection control messages

Send any of these fields to slmp-read or slmp-write:

Msg field	Effect
`msg.topic = "connect"`	Opens the shared connection.
`msg.topic = "disconnect"`	Closes the shared connection.
`msg.topic = "reinitialize"`	Closes and opens the shared connection.
`msg.connect = true`	Same as `connect`.
`msg.disconnect = true`	Same as `disconnect`.
`msg.reinitialize = true`	Same as `reinitialize`.

Metadata output

When Metadata is full, msg.slmp includes:

Field	Description
`msg.slmp.addresses`	Normalized read addresses. Present on `slmp-read`.
`msg.slmp.updates`	Normalized write updates. Present on `slmp-write`.
`msg.slmp.connection`	Connection profile with host, port, transport, PLC profile, frame type, series, target, and remote password status.
`msg.slmp.target`	Effective request target after route overrides.

When Metadata is minimal, msg.slmp includes only target, itemCount, and metadataMode.

When Metadata is off, the node leaves msg.slmp unchanged.

Error handling

Mode	Behavior
Throw	Calls Node-RED `done(error)` and lets the runtime route the error.
`msg.error`	Adds the error object to `msg.error` and sends the message on the normal output.
Second output	Sends the failed message with `msg.error` on output 2.

Unsupported device-code errors can be converted into skipped messages by sending msg.slmpSkipUnsupported = true or msg.slmp.skipUnsupported = true.