Mitsubishi Communication Protocols
MELSEC PLCs support three main communication protocols: SLMP (Seamless Message Protocol) — the modern, recommended approach for new integrations. MC Protocol (3E/4E frame) — the legacy protocol, still widely used. CC-Link — Mitsubishi proprietary fieldbus for device-level communication. For web/cloud integration, focus on SLMP over Ethernet.
Reading Data via SLMP
SLMP allows you to read device memory (D registers, M bits, Y/X contacts) directly over TCP/IP. Open a TCP socket to port 5007 on the PLC, send a properly formatted SLMP read request, and parse the response. The Python pymelsec library makes this straightforward.
Device Memory Map
Mitsubishi uses device names instead of register numbers: D registers for data words (D0–D9999), M bits for internal flags (M0–M2047), Y outputs for digital outputs, X inputs for digital inputs. Work with your machine documentation to map these device addresses to meaningful variable names in your integration layer.
Common Integration Patterns in Indian Factories
The most common use case we encounter: automotive factories with MELSEC Q series PLCs on assembly lines that need production count, cycle time, and fault code data fed into a web dashboard. We typically deploy a Raspberry Pi 4 per production line running our SLMP gateway, which aggregates data from 3–8 PLCs and publishes to MQTT.
Mitsubishi MELSEC integration is well-documented and reliable using SLMP over Ethernet. The pymelsec Python library or a Node.js equivalent handles most integration scenarios without any special hardware.
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