Windows

Set up PySerial on Windows with COM port discovery, driver installation, permissions, and Device Manager troubleshooting.

Windows uses COM ports (COM1, COM3, etc.) instead of /dev/tty*. PySerial handles this automatically.

Quick Windows Setup

Install Python and PySerial

Download Python from python.org and check "Add Python to PATH" during installation. Then open Command Prompt:

pip install pyserial

Find COM Ports

import serial.tools.list_ports

ports = serial.tools.list_ports.comports()
for port in ports:
    print(f"{port.device}: {port.description}")
    if port.vid:
        print(f"  VID:PID = {port.vid:04X}:{port.pid:04X}")

Test Connection

import serial

ser = serial.Serial('COM3', 9600, timeout=1)
ser.write(b'Hello Windows!')
response = ser.read(100)
print(f"Received: {response}")
ser.close()

Log serial data automatically

TofuPilot records test results from your PySerial scripts, tracks pass/fail rates, and generates compliance reports. Free to start.

COM Port Discovery

import serial.tools.list_ports

def find_com_ports():
    """List COM ports grouped by chip type."""
    ports = serial.tools.list_ports.comports()

    for port in ports:
        desc = port.description.lower()
        chip = "Unknown"
        if 'arduino' in desc:
            chip = "Arduino"
        elif 'ftdi' in desc or port.vid == 0x0403:
            chip = "FTDI"
        elif 'prolific' in desc or port.vid == 0x067B:
            chip = "Prolific"
        elif 'ch340' in desc or 'ch341' in desc:
            chip = "CH340"
        elif 'cp210' in desc:
            chip = "CP210x"

        print(f"{port.device}: {port.description} [{chip}]")
        if port.vid:
            print(f"  VID:PID = {port.vid:04X}:{port.pid:04X}")

find_com_ports()

# List COM ports
Get-WmiObject Win32_SerialPort | Select-Object DeviceID, Description, Status

# More detailed info (includes USB-serial adapters)
Get-WmiObject Win32_PnPEntity | Where-Object {$_.Caption -match "COM\d+"} |
    Select-Object Caption, DeviceID, Status, Manufacturer

Command Prompt alternative:

mode
wmic path Win32_SerialPort get DeviceID,Description,Status

Open Device Manager with Win+X or devmgmt.msc.

Check these sections:

Ports (COM & LPT): active COM ports
Universal Serial Bus controllers: USB-serial adapters
Other devices: unrecognized hardware (needs driver)

Troubleshooting indicators:

Yellow triangle: driver issue
Red X: disabled device
Question mark: unknown device

Driver Installation

USB-to-serial adapters need drivers on Windows. Download from the chip manufacturer for best compatibility.

Chip	Download	Notes
FTDI FT232/FT234X	ftdichip.com/drivers	Most reliable
CH340/CH341	Search "CH341SER driver"	Common on cheap boards
Prolific PL2303	prolific.com.tw	Clone chips cause issues, use official drivers only
CP210x	silabs.com/developers	Good Windows support

Connect the device. If it shows in "Ports (COM & LPT)" you already have the driver. If it shows in "Other devices", note the Hardware ID (right-click, Properties, Details) and install the matching driver above.

Install and Verify

Run the driver installer as Administrator.
Restart if prompted.
Reconnect the device and confirm it appears under "Ports".

Windows-Specific Configuration

Registry COM Port Info

import winreg

def get_registry_com_ports():
    """Read COM port mappings from the Windows registry."""
    key_path = r"HARDWARE\DEVICEMAP\SERIALCOMM"
    try:
        key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, key_path)
        i = 0
        while True:
            try:
                name, value, _ = winreg.EnumValue(key, i)
                print(f"{value} -> {name}")
                i += 1
            except OSError:
                break
        winreg.CloseKey(key)
    except OSError as e:
        print(f"Registry read failed: {e}")

get_registry_com_ports()

Buffer Sizes

import serial

ser = serial.Serial('COM3', 115200, timeout=1)

# Windows lets you request specific buffer sizes
ser.set_buffer_size(rx_size=8192, tx_size=4096)
print(f"Buffers configured, timeout={ser.timeout}s")

ser.close()

Disable USB Selective Suspend

At high baud rates, Windows USB power management can cause dropped data. Disable it in an elevated PowerShell:

powercfg /setacvalueindex SCHEME_CURRENT `
    2a737441-1930-4402-8d77-b2bebba308a3 `
    48e6b7a6-50f5-4782-a5d4-53bb8f07e226 0
powercfg /setactive SCHEME_CURRENT

Troubleshooting

Permission Denied

PermissionError: [Errno 13] usually means another program has the port open.

Close Arduino IDE, PuTTY, HyperTerminal, or any serial monitor.
Check Task Manager for processes holding the port.
If nothing obvious, try running Python as Administrator.
Some antivirus software blocks serial port access. Add Python to the exclusions list.

COM Port Keeps Changing

USB-serial adapters get a new COM number each time they're plugged into a different USB port.

Open Device Manager, right-click the port, Properties, Port Settings, Advanced.
Assign a fixed COM port number (avoid COM1-4, often reserved).
To clean up phantom ports: set environment variable DEVMGR_SHOW_NONPRESENT_DEVICES=1, open Device Manager, View, Show hidden devices, and uninstall grayed-out COM entries.

Port Won't Open

import serial
import serial.tools.list_ports
import platform

print(f"Windows {platform.win32_ver()[0]} {platform.win32_ver()[1]}")
print(f"Python {platform.python_version()}")
print(f"PySerial {serial.__version__}")

ports = list(serial.tools.list_ports.comports())
print(f"\n{len(ports)} serial port(s) found:")

for port in ports:
    print(f"\n  {port.device}: {port.description}")
    if port.vid:
        print(f"    VID:PID: {port.vid:04X}:{port.pid:04X}")

    try:
        s = serial.Serial(port.device, 9600, timeout=0.1)
        print(f"    Status: opens OK")
        s.close()
    except PermissionError:
        print(f"    Status: permission denied (another app has it open?)")
    except serial.SerialException as e:
        print(f"    Status: error - {e}")

If no ports appear at all, the driver is missing. Check "Other devices" in Device Manager and install the correct driver from the table above.