USB-Serial Adapter Connectivity

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


Be sure to use only the latest drivers with your USB-serial adapter. Even the drivers included with the adapter on CD may be out of date. While older drivers may work with older operating systems, they consistently create problems for users using Windows Vista or Windows 7.

If you purchased your USB-serial adapter through SymTech Laboratories (Sewell/Prolific chipset), you can download the manufacturer's latest drivers here:

If you are preparing to use a USB-serial adapter for the first time, download and run the appropriate driver installer before plugging in the adapter.


MS3 cards feature a built-in USB-serial adapter based on the FTDI chipset. Most Windows Vista and Windows 7 computers should automatically recognize this chipset and install the appropriate driver the first time you connect to your MS3 ECU via its USB port.

USB Port

Choose one USB port to use for tuning MegaSquirt and remember it. Many computers will not recognize the same USB-serial adapter if it is plugged into different USB ports. It is possible to circumvent this limitation by installing the same drivers for each USB port on your computer, but this step is unnecessary and bothersome.


Using the proper settings is crucial to successfully using your USB-serial adapter. Be sure to have the USB-serial adapter plugged into your USB port of choice. Also be sure the drivers 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/7

  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 USB-serial adapter in the resulting list. If you purchased your adapter from SymTech Labs, you should find an option similar to “Prolific USB-to-Serial Comm Port (COM1).”

Choosing the Correct Settings

  1. Select the “Port Settings.”
  2. Enter the following settings:
Setting MS1 MS2 MS3
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.”
  • If COM1 is marked as “in use,” take the following steps.
    • If your computer has a built-in serial port, assign the adapter to an unused COM port. Please note, however, that you should not require the use of a USB-serial adapter at all. In fact, you may find using an adapter more difficult if your computer has a standard serial port. Please see our article on serial port connectivity for directions on configuring a built-in serial port.
    • If there is another device in the “Ports (COM & LPT)” list set to COM1, follow the above mentioned steps in this section and reassign it to another number. Make a note of the new port for this device. Assign your USB-serial adapter to COM1.
    • If there are no other devices in the “Ports (COM & LPT)” list set to COM1, assign your USB-serial adapter to COM1 and ignore any subsequent warnings.



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