// LEARN

MC Protocol Guide

A step-by-step introduction to the MC protocol (SLMP), which lets a PC read and write Mitsubishi Electric PLCs — starting from what is inside each message. Useful whether you use a library or implement it yourself.

  1. 01 What is the MC protocol? How it relates to SLMP, and what it can do The MC protocol lets PCs and other external devices read and write the devices of Mitsubishi Electric PLCs. This article covers its relationship to SLMP, the frame types, and TCP versus UDP, based on the Mitsubishi Electric manuals.
  2. 02 Reading the 3E frame byte by byte (binary / ASCII) What sits at each byte of an MC protocol (SLMP) 3E frame request and response, read one byte at a time from an example in the Mitsubishi Electric manual — plus the little-endian pitfall, the ASCII variant and the iQ-R subcommands.
  3. 03 Reading MC protocol error codes (end codes): C059, C056, 4031 and more Where the end code sits in an MC protocol (SLMP) response, how to read it, and what the frequent error codes (C051, C056, C059, C05E, 4031 and others) mean and how to fix them, based on the Mitsubishi Electric manuals.
  4. 04 Raw MC protocol vs McpX vs MX Component, side by side in C# The same task — reading D100–D102 from a Mitsubishi Electric PLC — written three ways: building MC protocol messages by hand, the .NET library McpX, and Mitsubishi Electric's MX Component. Compare code size, setup, supported environments and where each fits.