FTDI Serial Troubleshooting

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Windows Serial Adapter Driver

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MAC OS Serial Adapter Driver

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Windows ARM Serial Adapter Driver

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Linux Serial Adapter Driver

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To Check and see if your adapter is installed:

Windows

Windows 8 / 8.1 / 10 / 11:

1. Right-click on the Start logo (or press Windows key + X)
2. Left-click on “Device Manager” from the menu
3. In Device Manager, expand the “Ports (COM & LPT)” section
4. Look for your serial device (may appear as “USB Serial Port”, “FT232 Serial Port”, “FTDI Serial Port”, “USB Serial Device”, or similar)
5. If the device is properly installed, it should show without any warning icons (yellow triangles or red X marks)
6. Note the COM port number (e.g., COM3, COM4) – this is what you’ll use in your serial terminal software
7. If you see a yellow warning icon, right-click the device and select “Update driver” or “Uninstall device” then reinstall

Windows XP & 7:

1. Click on Start
2. Right-Click on “My Computer” (This is just called “Computer” in Windows 7)
3. Left-Click on “Manage”
4. Device Manager is in the left Window, under System Tools
5. In Device Manager, expand the “Ports (COM & LPT)” section
6. Look for your serial device (may appear as “USB Serial Port”, “FT232 Serial Port”, “FTDI Serial Port”, “USB Serial Device”, or similar)
7. If the device is properly installed, it should show without any warning icons (yellow triangles or red X marks)
8. Note the COM port number (e.g., COM3, COM4) – this is what you’ll use in your serial terminal software
9. If you see a yellow warning icon, right-click the device and select “Update driver” or “Uninstall device” then reinstall

macOS

1. Open Terminal (Applications → Utilities → Terminal)
2. List all serial ports by running:

ls /dev/tty.* /dev/cu.*

3. Look for entries like /dev/tty.usbserial-XXXX or /dev/cu.usbserial-XXXX where XXXX is a unique identifier
4. For outgoing connections, use /dev/cu.* devices (e.g., /dev/cu.usbserial-XXXX)
5. Optional: To get more detailed USB information, run:

system_profiler SPUSBDataType | grep -i -A5 serial
# or
ioreg -p IOUSB -l | grep -i ftdi

6. If no serial devices appear, try unplugging and reconnecting the adapter, then run the ls command again

Linux

Most Linux distributions include FTDI support in the kernel via the ftdi_sio and usbserial drivers, so no separate driver installation is required.

1. Plug in the adapter and check the kernel log for detection:

dmesg | grep -i ttyUSB

2. List all serial devices:

ls -l /dev/ttyUSB* /dev/serial/by-id/

3. Devices typically enumerate as /dev/ttyUSB0, /dev/ttyUSB1, etc.
4. If you see a permissions error when trying to access the device, add your user to the serial group and re-log in:

sudo usermod -aG dialout $USER

5. After adding yourself to the dialout group, log out and log back in for the changes to take effect

FTDI Driver Cleaning and Reinstall

1. 1. Download the CDM Uninstaller HERE.
   2. Extract the zip file, or open the “CDMuninstallerGUI.exe” utility.
   3. Leave the ‘Vendor ID’ set to 0403 and ‘Product ID’ set to 6001.
   4. Click Add.
   5. Click Remove Devices.
   6. Download the corresponding driver for your operating system and follow on-screen prompts. Windows Driver | MacOS Driver

Changing Your Device’s COM Port

1. 1. Click on Start and navigate to the Control Panel
   2. Locate and click on Device Manager
   3. Under “Ports (COM & LPT)” you will find your serial device (may be listed as “USB Serial Port”, “FT232 Serial Port”, “FTDI Serial Port”, “USB Serial Device”, or similar) along with its current COM Port.
   4. Right click on your serial device and click on Properties.
   5. Navigate to the “Port Settings” tab and click on “Advanced…”
   6. Once there, the “COM Port Number:” can be changed with a dropdown menu to select the port number.
   7. Click your desired port number (i.e. COM2) and click “OK”.
   8. Click “OK” once more.
   9. Your serial device is now assigned to your chosen COM Port.

COM Port Settings Explained

These settings must match on both your computer and the connected device. Any mismatch can cause unreliable communication or no communication.

• Baud rate: Communication speed in bits per second. Common values: 9600, 19200, 38400, 57600, 115200. If mismatched, you will typically see garbled/jumbled characters or nonsense symbols.
• Data bits: Usually 8; some legacy or protocol-specific devices use 7. If mismatched, characters may appear truncated or incorrect.
• Parity: None (N), Even (E), Odd (O), Mark (M), Space (S). Most devices use None. A parity mismatch can cause intermittent missing characters and parity/framing errors.
• Stop bits: Typically 1; some devices require 2. If mismatched, expect framing errors or random-looking characters.
• Flow control: None, Hardware (RTS/CTS), or Software (XON/XOFF). If required but not enabled (or vice versa), you may see stalled transfers, buffer overruns, or missing data.

Tip: Check the manual or datasheet for the serial device you are connecting to for the exact settings it requires. If unknown, start with 9600 8-N-1 and adjust to match the device documentation.

Common symptoms of mismatched settings: jumbled or nonsense text, missing or extra characters, intermittent communication, framing/parity error messages, timeouts, or a failure to connect.

Typical default: 9600 baud, 8 data bits, No parity, 1 stop bit (often written as 8-N-1).

RS-232 Loopback Test (DB9)

Use a loopback test to quickly verify that your adapter, drivers, and terminal are working. For RS-232 DB9 connectors, TX and RX are on pins 3 and 2 respectively, and ground is on pin 5.

1. With the adapter unplugged, prepare a short wire or paperclip to bridge pins 2 and 3 on the DB9 connector. (Optional: also connect pin 5 to ground reference.)
2. Plug the adapter in and determine the COM port (see sections below for your OS).
3. Open a serial terminal to that port using the correct settings (baud, data bits, parity, stop bits, flow control).
4. Type on the keyboard. If pins 2 and 3 are jumpered, characters you type should echo back immediately. If not, recheck wiring and settings.
5. Remove the jumper when done. For RS-485/422 adapters, consult the product guide for proper loopback wiring.

Common Serial Communication Issues

No Communication

• Wrong COM port: Verify the correct port in Device Manager and your terminal application.
• Driver issues: Reinstall drivers if the device shows with a yellow warning icon in Device Manager.
• Wrong settings: Double-check baud rate, data bits, parity, and stop bits match your device.
• Device not powered: Ensure your serial device has adequate power supply.
• Wrong cable: Verify you’re using the correct cable type (straight-through vs. null modem).

Intermittent Communication

• Loose connections: Check all cable connections and ensure they’re secure.
• Electrical interference: Move cables away from power sources or fluorescent lights.
• Cable length: Long cables (>50 feet) may require lower baud rates or signal boosters.
• Ground loops: Ensure proper grounding between devices.

Garbled Data

• Baud rate mismatch: Most common cause – verify both devices use the same speed.
• Parity settings: Check if your device requires parity (most use None).
• Data bits: Confirm 7 vs 8 data bits setting.
• Stop bits: Verify 1 vs 2 stop bits configuration.

Serial Cable Types

Straight-through cables: Pins connect directly (1→1, 2→2, 3→3, etc.). Used when connecting a DTE (Data Terminal Equipment) to a DCE (Data Communications Equipment).

Null modem cables: Cross certain pins (2↔3, 4↔6, 7↔8). Used when connecting two DTE devices together.

Common mistake: Using a straight cable when a null modem is needed, or vice versa. If communication fails with one cable type, try the other.

Advanced Troubleshooting

Software Tools

• Port monitors: Use tools like Portmon (Windows) to monitor serial traffic.
• Signal generators: Test with known good signals to isolate hardware vs. software issues.
• Protocol analyzers: For complex protocols, use dedicated analysis tools.

Serial Terminal Applications

Important: Some serial devices require specific software or communication protocols to function properly. Before using a general terminal application, check your device’s manual or documentation to see if it requires proprietary software, specific commands, or special communication protocols. Common examples include industrial equipment, medical devices, and specialized hardware that may need manufacturer-provided software.

Windows

• PuTTY (Serial): Select “Serial”, set “Serial line” (e.g., COM3) and “Speed” (baud). Under Connection → Serial, set data bits, parity, stop bits, and flow control. Download at putty.org.

macOS

• screen (built-in):

screen /dev/tty.usbserial-XXXX 9600

Replace the device and baud as needed. To exit, press Ctrl+A, then K and confirm with Y (or Ctrl+A, then \ to quit).

Linux

• screen:

screen /dev/ttyUSB0 115200

• minicom:

sudo apt-get install minicom
minicom -D /dev/ttyUSB0 -b 115200

• picocom:

sudo apt-get install picocom
picocom -b 115200 /dev/ttyUSB0

Ensure the terminal settings (baud, data bits, parity, stop bits, flow control) match your device.