gomcprotocol

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A Go library for communicating with Mitsubishi PLCs using the MC Protocol (SLMP).

Features

• 3E frame — TCP and UDP transport, Binary and ASCII mode
• 4E frame — TCP, Binary and ASCII mode, with serial number tracking
• Batch read/write: words and bits
• Random read/write: multiple devices in a single request
• Remote control: Run, Stop, Pause, Latch Clear, Reset
• Goroutine-safe: requests on the same client instance are serialized internally

REST Wrapper API

A REST API wrapper for this library is available at Moge800/gomc-rest. Use it when you want to expose MC Protocol communication over HTTP from another application or service.

Installation

go get github.com/moge800/gomcprotocol

import "github.com/moge800/gomcprotocol"

Quick Start

3E frame (TCP)

package main

import (
    "fmt"
    mc "github.com/moge800/gomcprotocol"
)

func main() {
    c, err := mc.New3EClient("192.168.0.1", 5007, mc.ModeBinary)
    if err != nil {
        panic(err)
    }
    if err := c.Connect(); err != nil {
        panic(err)
    }
    defer c.Close()

    // Read 5 words from D100
    words, err := c.ReadWords("D", 100, 5)
    if err != nil {
        panic(err)
    }
    fmt.Println(words)

    // Write to D200
    if err := c.WriteWords("D", 200, []uint16{1, 2, 3}); err != nil {
        panic(err)
    }
}

3E frame (UDP)

c, err := mc.New3EClientUDP("192.168.0.1", 5007, mc.ModeBinary)

4E frame

c, err := mc.New4EClient("192.168.0.1", 5007, mc.ModeBinary)

API Reference

Client3E

Method	Description
New3EClient(host, port, mode)	Create a 3E TCP client
New3EClientUDP(host, port, mode)	Create a 3E UDP client
Connect()	Establish connection
Close()	Close connection
ReadWords(device, start, count)	Read word values
WriteWords(device, start, values)	Write word values
ReadBits(device, start, count)	Read bit values
WriteBits(device, start, values)	Write bit values
RandomRead(words, dwords)	Read multiple devices at once
RandomWrite(words, wordVals, dwords, dwordVals)	Write multiple devices at once
RandomWriteBits(devices, values)	Write multiple bit devices at once
RemoteRun(clearMode, force)	Start PLC remotely
RemoteStop()	Stop PLC remotely
RemotePause(force)	Pause PLC remotely
RemoteLatchClear()	Clear latch (PLC must be stopped)
RemoteReset()	Reset PLC (connection will close)

Client4E provides the same methods as Client3E, created via New4EClient.

Requests issued concurrently on the same client instance are serialized internally, so only one MC Protocol request/response exchange is active on that connection at a time.

Modes

Constant	Description
ModeBinary	Binary framing (compact, recommended)
ModeASCII	ASCII framing (human-readable)

Supported Devices

Device	Type	Notes
D	Word	Data register
W	Word	Link register
R	Word	File register
ZR	Word	File register (extended)
SW	Word	Link special register
TN	Word	Timer current value
STN	Word	Retentive timer current value
CN	Word	Counter current value
Z	Word	Index register
X	Bit	Input
Y	Bit	Output
M	Bit	Internal relay
L	Bit	Latch relay
V	Bit	Edge relay
S	Bit	Step relay
DX	Bit	Direct access input
DY	Bit	Direct access output
TC	Bit	Timer coil
TS	Bit	Timer contact
STC	Bit	Retentive timer coil
STS	Bit	Retentive timer contact
CC	Bit	Counter coil
CS	Bit	Counter contact
B	Bit	Link relay
F	Bit	Annunciator
SB	Bit	Link special relay
SM	Bit	Special relay
SD	Word	Special register

Device names are case-insensitive ("d" and "D" both work).

Random Access

// Read D100 (word) and D200 (word) and D300 (dword) in one request
words, dwords, err := c.RandomRead(
    []mc.DeviceAddr{{"D", 100}, {"D", 200}},
    []mc.DeviceAddr{{"D", 300}},
)

// Write D100=10, D200=20 (words) and D300=100000 (dword)
err = c.RandomWrite(
    []mc.DeviceAddr{{"D", 100}, {"D", 200}},
    []uint16{10, 20},
    []mc.DeviceAddr{{"D", 300}},
    []uint32{100000},
)

// Write bits to M0, M10, Y5
err = c.RandomWriteBits(
    []mc.DeviceAddr{{"M", 0}, {"M", 10}, {"Y", 5}},
    []bool{true, false, true},
)

Error Handling

words, err := c.ReadWords("D", 100, 5)
if err != nil {
    if mcErr, ok := err.(*mc.MCProtocolError); ok {
        // PLC returned a non-zero end code
        fmt.Printf("PLC error: 0x%04X\n", mcErr.EndCode)
    } else {
        // Network or connection error
        fmt.Println("connection error:", err)
    }
}

PLC Setup

The PLC must have Ethernet communication enabled with SLMP (MC Protocol) configured.
Default port is typically 5007 for Q/iQ-R series.

Examples

Runnable examples are in the examples/ directory:

Directory	Description
01_basic_read	Read word devices (minimal)
02_basic_write	Write words and read back
03_bit_operations	Read/write bit devices (X, M, Y)
04_random_access	RandomRead/RandomWrite across multiple devices
05_remote_control	Stop → LatchClear → Run sequence
06_monitor	Polling loop with change detection and auto-reconnect

License

MIT