Serial Port Connectivity

Here are a few tips and tricks for successfully connecting to your MegaSquirt ECU using your computer's built-in serial port. Please see our article on USB-serial adapter connectivity for information on connecting to your MegaSquirt ECU using a USB-serial adapter.


Using the proper settings is crucial to successfully using your built-in serial port. Be sure the latest drivers and updates are correctly installed before attempting to adjust any settings.

Finding the Device Manager

Finding the settings varies slightly depending on the operating system.

Windows Vista

  1. Click the Windows Start button in the lower left corner of your screen.
  2. Type “device manager” in the “Start Search” field, then hit “Enter.”
  3. Click “Continue” or “OK” if prompted by any security warnings.

Windows XP

  1. Right-click on “My Computer,” usually found on the desktop or Start Menu, then click “Properties.”
  2. Select the “Hardware” tab, then click “Device Manager.”


  1. Click the “Start” button, and then “Control Panel.”
  2. Double-click on “System.”
  3. Select the “Hardware” tab, then click “Device Manager.”

Once in the device manager, click the ”+” sign next to “Ports (COM & LPT).” Find your serial port in the resulting list. You should find an option similar to “Serial Port (COM1).”

Choosing the Correct Settings

  1. Select the “Port Settings.”
  2. Enter the following settings:
Setting MegaSquirt-I MegaSquirt-II
Bits per second: 9600 115200
Data bits: 8
Parity: None
Stop bits: 1
Flow control: None
  1. Click “Advanced…”
  2. Ensure the “Use FIFO buffers” checkbox is checked.
  3. Drag the sliders corresponding to the “Receive Buffer” and “Transmit Buffer” to their lowest positions, either “0” or “1.”
  4. Ensure the “COM Port Number” is set to “COM1.”
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