AiVibeMitsubishi MC Protocol
MC protocol (MELSEC Communication protocol) is Mitsubishi Electric's protocol that lets external devices such as PCs, HMIs and gateways read and write device memory in MELSEC programmable controllers over Ethernet or serial connections.
With MC protocol, an external client sends commands to a MELSEC CPU or communication module to read or write device memory, including bit devices and word devices identified by device type and number. Several frame formats are defined, of which the 3E and 4E frames are commonly used over Ethernet, and data can be encoded in binary or ASCII. Ethernet communication runs over TCP or UDP on ports configured in the PLC, and serial variants exist for RS-232 and RS-422/485 links.
MC protocol is widely used to connect MELSEC controllers to SCADA, HMIs, MES and IIoT systems, because once the communication port is configured it allows data collection without changing the PLC program. Mitsubishi Electric also documents SLMP (SeamLess Message Protocol), which is closely related to MC protocol.
Engineers must match the frame type, binary or ASCII code, port numbers and transport (TCP or UDP) on both sides, and confirm from Mitsubishi documentation which devices and address ranges a given CPU supports. Classic MC protocol has no strong authentication, so write access should be avoided unless required, and networks should be segmented following IEC 62443. Configuration changes must be made by qualified personnel under change control.
Key points
- Mitsubishi Electric protocol for reading and writing MELSEC device memory
- 3E and 4E frames are common over Ethernet, in binary or ASCII code
- Runs over TCP or UDP on ports configured in the PLC; serial variants exist
- SLMP is a closely related Mitsubishi Electric protocol
- No strong authentication; restrict writes and segment networks
Where AiVibe comes in
AiAmbA IoT lists Mitsubishi MC among its supported protocols, with driver availability confirmed per installation and writes to machines deny-by-default.