I2C Error

Times to times I am getting an error of type I2C related to one of the motors. It will be horrible if it happens in the middle if the competition. The connections to the motors are good and the error is random. I added some sleep time in my while loop which seems improving the situation a bit.


We are sorry that you are having this problem. Are you running the built-in Driver Control program or are you using a custom program? If you are using a custom program, are you using RobotC or Modkit?

If you are using RobotC you should upgrade to at least version 4.06. Earlier versions of RobotC had the potential to cause I2C errors by communicating with the sensors too quickly. There is more information about this update in the following thread:


  • Art

Our team still has this problem sometimes, with v4.06 of RobotC.


We’re working with ROBOTC to further improve performance and try to eliminate this problem completely. Hopefully we can get out a new version of the firmware which solves this within the next 2 weeks.

I am using 4.06 and we have times to times this error. I hope it will not happen during the science Olympiad this week.

We are getting it from time to time with v4.06, but not as often as previous versions.

In good news - we have new firmware from VEX that seems resolve issues with the Controller/Radio and I2C interrupts interfering with each other. We are currently testing this firmware internally, but our initial tests show 10hr of maximum I2C traffic without any crashes/errors. Hopefully we’ll be able to release this new firmware very soon!

tfriez - How will we know where the new release is ready? Where should we look?


If you are signed up to recieve the email notifications you will get a reminder in your inbox, jrp62. Just visit the download software page to sign up for updates.

Thanks Tim, cause I want to download it as soon as available.

Our robot also had many I2C errors throughout 2013. Glad to hear the RobotC team is working on a fix.

It looks like a new VEXiq V1.11 was released : http://www.vexrobotics.com/vexiq/software/firmware

And V4.10 RobotC has also been released: http://www.robotc.net/download/vexrobotics/

I don’t see any updates about I2C fixes from the changelog. http://www.vexrobotics.com/vexiq/software/firmware/changelog


The Robot Brain firmware version 1.09 contained the bug fix for the I2C errors that were occurring in RobotC. The old pre-1.09 firmware would intermittently miss some I2C traffic due to the radio bus speed, which would cause an I2C error. This issue did not cause widespread problems in Modkit as their previous threading system only ran each thread once every 25ms so there was significantly less I2C traffic.

The next version of the Robot Brain firmware will also contain hot-swapping capability so that the Robot Brain will not need to be rebooted if any motors or sensors are plugged in or removed. With hot swapping, all I2C devices will be reinitialized every time a program runs. In the rare event that an I2C error occurs, you will be able to correct the issue entirely from your Controller. Here is a screenshot from the newest version of the VEX IQ user guide that will ship with new kits later this summer (and will be posted on our website soon):

Thus, you can double tap the power button to exit a running program, then press the F▲ button to run the last selected program


  • Art