Proteus Troubleshooting

This page picks up where the Proteus Walkthrough ends. Work through it top to bottom on a new machine, or jump to the troubleshooting table if you already have an error.

How the pieces connect

Windows lets only one program open a COM port at a time. Proteus's COMPIM holds its port, so your master script can't open that same port. Instead, you create a virtual null-modem pair: two linked COM ports where anything written to one comes out of the other. Proteus opens one end, and your master opens the other.

Arduino (in Proteus) ──UART── COMPIM ── COM1 ⇄ COM12 ── SerialTransport ── MasterDevice ── MQTT ── Nexalware
                                          └─ com0com pair ─┘

You need one pair per sub-device. The examples on this page use:

Any free port names work. How to choose them is covered below.

1. Install com0com (signed build)

Use com0com 2.2.2.0, the signed x64 build: com0com-2.2.2.0-x64-fre-signed.zip from SourceForge.

To check which version you have, open C:\Program Files (x86)\com0com\com0com.inf and look at the DriverVer line. It should end in 2.2.2.0. If it says 3.0.0.0:

1. In the com0com Setup Command Prompt, remove the existing pairs (remove 0, remove 1, …).
2. Uninstall com0com and restart Windows.
3. Install the signed 2.2.2.0 build. Untick the default CNCA0 <-> CNCB0 pair during setup.

If SetupG.exe (the GUI configuration tool) shows a pair but Windows Device Manager doesn't list the port, check its "use Ports class" checkbox for both sides of that pair, then click Apply - without it, the port exists in com0com's own config but never registers under Windows's standard "Ports (COM & LPT)" class, which is what SerialTransport/Device Manager both look for.

2. Pick free port names

List the ports Windows already has:

[System.IO.Ports.SerialPort]::GetPortNames()
Get-CimInstance Win32_PnPEntity | Where-Object Name -match '\(COM\d+\)' | Select-Object Name, Status

Two things to watch for:

• Some ports belong to real hardware. On many laptops COM3 is Intel Active Management Technology – SOL, a built-in device, not something com0com or Proteus created - closing Proteus won't free it. A USB-serial adapter you once plugged in can also keep its number (for example COM4) even when it's unplugged. If com0com or Proteus reports a port as busy and closing Proteus doesn't fix it, check Device Manager for a real device already using that name (its error message often names the underlying device, e.g. /Device/Serial0, which is Windows's own name for onboard hardware) - pick a different, unused number instead of fighting for that one. Numbers above COM10 are almost always free.
• Older Proteus versions only list COM1–COM4 in the COMPIM port dropdown. Give the Proteus end of each pair a low number (COM1, COM2), and the master end any free number (COM12, COM14).

3. Create the pairs

Open Start → com0com → Setup Command Prompt with right-click → Run as administrator, then run:

install PortName=COM12 PortName=COM1
install PortName=COM14 PortName=COM2
list

list should show:

CNCA0 PortName=COM12
CNCB0 PortName=COM1
CNCA1 PortName=COM14
CNCB1 PortName=COM2

Lines like ComDB: COM1 - logged as "in use" right after install are normal: com0com is reserving the names.

If you prefer PowerShell (as Administrator), call setupc.exe directly. The .\ is required:

cd "C:\Program Files (x86)\com0com"
.\setupc.exe install PortName=COM12 PortName=COM1
.\setupc.exe install PortName=COM14 PortName=COM2

If install says The port name COM12 is already logged as "in use", a pair using that name already exists. Run list to see it. Either use it as it is, or rename one end with change, for example:

change CNCB0 PortName=COM1

If it instead says the port is in use by another device (not a com0com pair), fully close Proteus first (COMPIM holds its port for as long as Proteus is open, not just while the simulation is running) and retry. If it's still busy after Proteus is closed, that name belongs to real hardware - see step 2 and pick a different one.

Confirm Windows can see all four ports:

[System.IO.Ports.SerialPort]::GetPortNames()   # should include COM1, COM2, COM12, COM14

Close and reopen Proteus after creating or renaming ports. It only reads the port list at startup.

4. Configure each circuit in Proteus

For each Arduino + COMPIM circuit:

COMPIM properties

Arduino properties

The sketches use JsonDocument, so they need ArduinoJson v7 (Library Manager → ArduinoJson). With v6 the sketch won't compile, and Proteus will silently keep running whatever old .hex it had.

Checking the wiring. Add a Virtual Terminal (Instruments) with its RXD on the Arduino's TX (D1), set to 9600 baud, and press Play. You should see the sketch's identify, describe and state lines. If the terminal shows them but the master receives nothing, the COMPIM's TXD/RXD connections are the wrong way round - swap them. If the terminal is blank, the Arduino isn't running the sketch: check the Program File, the clock and ArduinoJson.

5. Startup order

The Proteus Walkthrough's reference sketch already re-announces identify/describe/state on a timer, not just once in setup() - a master only learns a sub-device exists from identify, so without re-announcing, starting the master after Proteus (or restarting either one mid-session) leaves that sub-device invisible until the simulation restarts. If you're working from an older copy of the sketch that only sends identify once, either add the timer (shown in the walkthrough) or always start the master first, then press Play in Proteus.

6. Debug logging

When something isn't reaching its destination, log both directions of every serial port. You can then tell exactly which hop is failing:

master.on("subDeviceSend", (channelId, message) => console.log(`-> ${channelId}: ${message}`));
const receiveForLog = master.receiveSubDeviceMessage.bind(master);
master.receiveSubDeviceMessage = (channelId, raw) => {
  if (channelId.startsWith("COM")) console.log(`<- ${channelId}: ${raw.trim()}`);
  receiveForLog(channelId, raw);
};

A healthy command looks like this:

-> COM12: {"type":"command","cmd":"ON"}
<- COM12: {"type":"result","cmd":"ON","ok":true}
<- COM12: {"type":"state","relay":"ON"}

To check whether Proteus actually has a port open, try opening it yourself. If Proteus holds it, you'll get "Access denied":

foreach ($p in 'COM1','COM2') {
  $s = New-Object System.IO.Ports.SerialPort $p,9600
  try { $s.Open(); "$p : free - Proteus is NOT using it"; $s.Close() } catch { "$p : busy (Proteus has it)" }
}

Troubleshooting table

See @nexalware/mcp's README for Windows-specific MCP connection issues (PowerShell quoting, npx timeouts, stale server processes).