S7 Communication Suite

The Problem

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Siemens S7 PLCs are everywhere in industrial automation — but connecting them to Node-RED has always been a trade-off. Pure JavaScript libraries work without native compilation but lack advanced features. Native Snap7 bindings offer full protocol support but are harder to install. And during development, you often don’t have a real PLC available at all.

The Solution

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A Node-RED package for Siemens S7 communication that lets you choose your backend — pure JS, native Snap7, or a built-in simulator — without changing your flows. Written in TypeScript for type safety and reliability.

blanpa/node-red-contrib-s7-suite

node-red-contrib-s7-suite

TypeScript

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1

Three Backends, One API

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Switch backends in the config node — your flows stay the same.

6 Nodes

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• s7-config — Manages PLC connections with backend selection and auto-reconnection; host, rack, slot, TSAPs and timeouts can each come from an environment variable, so one flow runs against different PLCs
• s7-read — Read multiple PLC addresses in a single request, with bulk tag import from TIA Portal and STEP 7 exports
• s7-write — Write data to PLC memory with dynamic addressing
• s7-trigger — Polling with edge detection and deadband filtering
• s7-browse — Discover available data blocks with filtering
• s7-control — CPU control operations (start, stop, cold start)

Supported Controllers

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S7-200, S7-300, S7-400, S7-1200, S7-1500, and LOGO!

Address Formats

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Three addressing styles — use whichever you’re comfortable with:

• nodes7-style: DB1,REAL0
• IEC-style: DB1.DBD0
• Area-style: MW4, I0.1, QD8

A number after the offset is an array length — DB1,INT20.3 is three integers, DB1,X10.3.8 eight consecutive bits — read as an array and written from one. For a string it is the declared length: DB1,STRING50.20 is a STRING[20] at offset 50.

Data Types

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25 types across the backends, each arriving in Node-RED as the value a flow would want rather than as bytes:

• Numbers — BYTE, WORD, INT, DWORD, DINT, REAL, LREAL, and the unsigned USINT, UINT, UDINT
• 64-bit integers — LINT and ULINT as Number, BigInt or String, chosen per connection, because a JavaScript number is exact only up to 2^53
• Dates and times — DT and DTL as a Date, in the PLC’s local time or as UTC (DTZ, DTLZ); DATE, TIME, TIME_OF_DAY and S5TIME
• Strings — STRING and WSTRING; a write changes only the current length and characters, never the declared length or the bytes after it

The pure-JS backend covers the common subset and refuses the rest with an error that names the address — never a silent null. Snap7 and the simulator support every type.

Tag Import

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Tag lists go into the read node in one step: a TIA Portal tag table export (.xlsx, .xml or .sdf), SimaticML from TIA Portal Openness, STEP 7 symbol exports, or a STEP 7 V5 hardware configuration — the last one without a live PLC connection, which is what makes engineering a flow offline possible.

Reliability

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• Request queuing (max 100 concurrent)
• Exponential backoff reconnection, and a link check while idle so the node status follows the PLC
• A read with some bad addresses still delivers the good ones and names the rest with the reason
• Edge detection for boolean values
• Deadband filtering to reduce noise

Quality

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• Written in TypeScript with strict type checking
• Jest test suite with 80% coverage threshold
• Docker support for containerized deployment
• Twelve of the pull requests in 0.0.9 came from an outside contributor — the editor, both backends, the new data types and the connection handling