How do I know which driver my USB serial adapter needs?

Open Device Manager, find the device (often under Other devices with a yellow triangle), open Properties → Details → Hardware Ids. VID_1A86 means CH340/CH341, VID_0403 means FTDI, VID_067B means Prolific. Install the matching vendor driver.

Why does my Prolific adapter say 'this device cannot start (code 10)'?

Usually a counterfeit PL2303 chip. Newer official Prolific drivers deliberately refuse fake chips. The workaround is installing an older driver version (3.8.x) and pinning it, or replacing the adapter with a genuine FTDI-based one.

How can I test a COM port without connecting a real Modbus device?

Install a virtual COM port pair (com0com), run a Modbus slave simulator on one end, and connect your master application to the other. If the simulated link works, your software stack is fine and the problem is the physical adapter or wiring.

Does Windows 11 handle USB serial adapters differently from Windows 10?

Windows 11 ships newer in-box drivers for CH340 and FTDI, so many adapters work out of the box. But it is also stricter about unsigned drivers, which breaks some older Prolific and clone-chip adapters that still worked on Windows 10.

July 12, 2026 · Troubleshooting

USB to Serial COM Port Not Showing in Windows 10/11: Complete Fix Guide

Q: Why is my USB to serial adapter not showing a COM port?

The most common causes are a missing or wrong chipset driver (CH340, FTDI, or Prolific), a counterfeit chip rejected by the official driver, a charge-only USB cable, or Windows hiding the port after a driver conflict. Device Manager tells you which case you have.

Adapter plugged in, device blinks, and still no COM port in Device Manager. This guide walks through every cause in order of probability — driver by driver — and shows you how to prove the port works once it appears.

Download Modbus Simulator Free Modbus RTU vs TCP Guide

First: Find Out What Windows Actually Sees

Open Device Manager (right-click Start → Device Manager) with the adapter plugged in, and look in three places:

Ports (COM & LPT) — if your adapter is here with a COM number, the port exists and your problem is elsewhere (wrong COM number in your app, or another program holding the port).
Other devices — a yellow-triangle entry like "USB-SERIAL CH340" or "USB Serial Port" means Windows sees the hardware but has no driver. This is the most common case; jump to the driver section.
Nothing appears at all — not even a sound when you plug in. That points to the cable or the adapter itself, not Windows: try another USB cable (many are charge-only), another USB port (prefer a rear motherboard port over a hub), and watch whether Device Manager refreshes.

To identify the chipset, open the device's Properties → Details → Hardware Ids. The VID tells you everything:

Hardware ID contains	Chipset	Driver you need
VID_1A86	WCH CH340 / CH341 (most cheap adapters)	WCH CH341SER driver
VID_0403	FTDI FT232R and family	FTDI VCP driver (usually auto-installs)
VID_067B	Prolific PL2303	Prolific driver — version matters, see below
VID_10C4	Silicon Labs CP210x	SiLabs CP210x VCP driver

Fixes by Chipset

CH340 / CH341 (VID_1A86)

Windows 11 usually installs this in-box now; Windows 10 often doesn't. Download CH341SER from the WCH site (or a mirror you trust), install, replug. If the device shows but the port errors, uninstall the device in Device Manager with "delete driver" checked, replug, and let the fresh driver bind. CH340 adapters are also the most sensitive to USB3 ports — if it's flaky on a blue port, move it to a USB2 port.

FTDI (VID_0403)

FTDI drivers install through Windows Update automatically on both Windows 10 and 11. If yours shows as "USB Serial Converter" but no COM port appears: Properties → Advanced → tick "Load VCP", then replug. If the device reports FT232R USB UART but reads garbage, you may have a counterfeit FTDI chip — the official driver once zeroed the PID on fakes (the infamous "FTDIgate"); such bricked units show PID_0000 in Hardware Ids and need a re-flash utility or replacement.

Prolific PL2303 (VID_067B)

The #1 source of "this device cannot start (Code 10)" and "PL2303 phased out, contact supplier" errors. Newer official drivers deliberately reject counterfeit and legacy chips — and a large share of PL2303 adapters sold online are counterfeit. Fix: install an older driver (3.8.x series), then in Device Manager → Update driver → "Browse my computer" → "Let me pick", select the old version, and hide it from Windows Update so it doesn't get replaced. Long term: replace Prolific adapters with FTDI or CH340 units — they're the same price and far less painful.

Any chipset: the port appeared, then vanished

Windows sometimes keeps a ghost of the old COM number. In Device Manager choose View → Show hidden devices, uninstall the grayed-out entries under Ports, then replug. If an app says "COM3 in use" but nothing is open, that ghost (or a background app like a 3D-printer or GPS utility) is holding it.

Now Prove the Port Actually Works

A COM number in Device Manager doesn't guarantee working communication — wiring (TX/RX swapped, missing ground, A/B reversed on RS-485), baud rate, and framing all still have to be right. The fastest way to separate "my software stack works" from "my wiring is wrong" is to test against a simulated device first:

1. Create a virtual pair

Install com0com and create a virtual COM pair (e.g. COM20 ↔ COM21). No hardware involved.

2. Run a simulated slave

Point a Modbus slave simulator at one end of the pair, your master application at the other.

3. Poll it

If reads succeed on the virtual pair but fail on the real adapter, your software and framing are fine — the problem is the physical layer: wiring, termination, or the adapter itself.

Modbus Simulator makes this workflow one screen: it can act as RTU master and slave, auto-detects the COM port, baud rate, and slave ID on the master side, and shows raw frames so you can see exactly what's on the wire. The RTU vs TCP guide covers the framing details, and if you're deciding between test tools, see the 2026 simulator comparison.

FAQ

Why is my USB to serial adapter not showing a COM port?

Missing/wrong chipset driver, counterfeit chip rejected by the official driver, a charge-only USB cable, or a hidden/ghost port. Device Manager's Hardware Ids identify which case you have.

Which driver does my adapter need?

Check the VID in Hardware Ids: VID_1A86 = CH340, VID_0403 = FTDI, VID_067B = Prolific, VID_10C4 = CP210x. Install the matching vendor driver.

What does "this device cannot start (Code 10)" mean on PL2303?

Almost always a counterfeit Prolific chip being refused by the new driver. Pin an older 3.8.x driver or replace the adapter with an FTDI-based one.

How do I test Modbus RTU without a real device?

com0com virtual COM pair + a Modbus slave simulator on one end. If that works and the real adapter doesn't, the issue is physical: wiring, A/B polarity, termination, or the adapter.

Is Windows 11 better or worse for USB serial?

Better for CH340/FTDI (in-box drivers), worse for old Prolific and clone chips (stricter driver signing).

Test Your Serial Setup Without Hardware

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