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MicroSquirt® Embedded Code

This page is out-of-date. It is preserved here only for archival purposes. Please see the updated page at:

This archive document primarily applies to older V2 and V1 MicroSquirt® controllers.
For the latest V3 MicroSquirt® controller documentation, click this link: V3 MicroSquirt® Quickstart Guide

For the latest code for your MicroSquirt® controller, see:

MicroSquirt® can use the same embedded code as MegaSquirt-II, and you can use any of the V2 code versions intended for the C64 version (with CAN) of the processor. However, MicroSquirt® has a few of its own specialized hardware functions (dual spark is the main function) and these are only implemented in code version 2.8 and higher.

Unlike MegaSquirt-II, MicroSquirt® comes with the embedded code already loaded onto its processor. You can still upgrade to newer versions of the code as they are released, of course, but you won't have to load the code initially to get MicroSquirt® working.

The current 'release' code for the MicroSquirt® controller is V3.780.

The 'ready to load' .s19 file for uploading to MegaSquirt-II(CAN) is here:

(Right click and 'Save As')

For the V2.890 code, you will need to download and activate the latest megasquirt-II_3780.ini file (right click the link and 'save as' to your project folder, then rename it to 'megasquirt-II.ini').

You will also want to copy the settings.ini file to your project's \mtCfg\ folder (usually 'C:Program Files\MegaSquirt\Car1\mtCfg\'). It will solve the "Conditional check references undefined value n2o" and "Conditional check references undefined value 'EXPANDED_CLT_TEMP'" errors.

You can also get the latest code and INI using the V2.0 downloader, which will get the code from the internet, and load the code to MicroSquirt® as well as installing/activating the matching INI. There's more info here:

To load the .S19 file to your MicroSquirt® over the serial port, you need to use Eric Fahlgren's latest MegaSquirt-II downloader program (click the link to download).

To use the downloader.exe:

  1. Power down MegaSquirt® EFI Controller,

  2. Ground the bootloader wire (Ampseal pin #15).

  3. Power up your MicroSquirt® controller.

  4. Start the downloader program (make sure TunerStudioMS is not running), and select the appropriate COM port. Note that 'File/Update' does not work on the downloader to fetch the latest code and INI anymore. You can get the latest code and matching INI from this link:

  5. Select the appropriate .S19 file using 'File/Open', and the downloader will read, write and verify the code to the processor in about 10 seconds or so. If you have a problem connecting to the controller, see the tips here:

  6. The process ends with a message like "Verification succeeded, 999 records total (4 skipped)."

  7. Shut down the downloader program.

  8. Remove power from your MicroSquirt® controller.

  9. Remove the bootloader wire from its ground connection.

  10. Start the tuning software (TunerStudioMS) and set the COM port and speed if necessary.

  11. You will need to download and activate the latest INI file. Under the 'File/Project/Project Properties' of TunerStudio, click on the Other check box.

  12. Click the 'Browse' button.

  13. Locate the INI file you downloaded for the link above (

  14. Click on the appropriate INI file you download from the code page ( to activate it.
See the readme file in the downloader package for more details.

You should recreate your settings file from scratch by entering the values by hand into MegaTune.

MegaSquirt® and MicroSquirt® controllers are experimental devices intended for educational purposes.
MegaSquirt® and MicroSquirt® controllers are not for sale or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a MegaSquirt® or MicroSquirt® controller is legal for your application.
©2005, 2012 Bruce Bowling and Al Grippo and Lance Gardiner. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of MegaSquirt® boards from Bowling and Grippo.