Does it behave exactly like a real PLC?

No. It follows the message formats in the public manuals and has not been compared with real hardware. No ladder program runs, and error codes, timing, connection limits and per-model device ranges may differ.

How do I connect an HMI on another PC?

Turn on «Allow other PCs to connect (0.0.0.0)» and allow the program in Windows Firewall. Do not run it on a plant network with the same IP and port as a real PLC.

PortDock PLC Simulator

The PC answers MC protocol (SLMP) requests like a PLC's Ethernet port. Put values in the device tables and HMI, data-collection or host software can read and write them; deliberate delays and error end codes test its error handling. It follows the message formats in Mitsubishi Electric's public manuals (SLMP/MC); it is not affiliated, and behaviour may differ from a real PLC.

Free · Windows 10 and 11 · no ads in the program · open source (GPL-3.0)

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PortDock PLC Simulator screen — MC protocol (SLMP) server simulator for testing without a PLC — Example screen with sample data. Click to enlarge.

Made for

Teams preparing HMI screens and communication before the PLC arrives
Developers of data-collection or host software that reads PLCs over the MC protocol

Features

3E/4E, binary/ASCII, TCP/UDP

Listens as a TCP server (several clients) or on UDP. 4E replies carry the request's serial number. By default only this PC (127.0.0.1) can connect; allowing other PCs is your choice.

Implemented commands

0401 Read and 1401 Write (words and bits, subcommands 0000–0003), 0403 Read Random, 1402 Write Random and 0619 Loopback. From 0.6.0 also 0406/1406 Read/Write Block, 0801/0802 monitor, 1001–1006 remote RUN/STOP/PAUSE/latch clear/reset (simulated state only) and 0101 Read Type Name (simulated values). Other commands get end code C059.

Condition rules (from 0.6.0)

Mimic handshakes such as «when the request bit turns on, turn the done bit on 300 ms later»: condition (bit ON/OFF/edge, word comparison, periodic) → delay (fixed or random) → actions (bit and word writes). Not a ladder program.

18 devices

X, Y, M, L, F, B, SM, D, W, R, ZR, SD, TS, TC, TN, CS, CC and CN. X, Y, B, W and ZR use hex numbers; each device has a size and requests beyond it get C056. Bit devices can be viewed as 16-point words; cells can be 32-bit, float, string or named.

Fault injection

Response delay (with a range), no response or a chosen end code — targeted by command, device, every Nth request or probability.

Decoded traffic

Each request shows the command name, device and points; each reply the end code and its meaning. Cells changed by a client flash, with statistics.

Simulation and saved states

Values can change by themselves (increment, random, sine, ramp, toggle), and device values and cell settings save to and load from a JSON file.

In every app — the «AI» button in the title bar (0.8.0, copy for asking AI): builds text for an AI chat from the program, connection settings, errors in this session and recent traffic (or check results), shows a preview and puts it on the clipboard only. PortDock sends nothing; once pasted, it goes to that AI service. User folders, PC names, the last half of MAC addresses and public IPs are masked. Privacy policy →

Quick start

Match the frame (3E/4E), data code (binary/ASCII) and port with the client
Pick a device (D, M, X …) and enter values
«Start» — client reads and writes are answered from the tables

Read the full guide →