Quadrature sensor not working when plugged in cortex port 4

I have three quadrature encoders plugged into the cortex, and 11 out of the 12 digital ports are being used. When I plug these quad encoders into different ports and ‘open debugger manually’ in robotC to view sensor values, the encoder which has a wire plugged into port 4 can have invalid values of -1, 0 or 1.

Here are the steps to reproduce the error.

  1. Plug the three encoders in port 1&2, 3&4, 5&6, the middle one works some time, but no longer working after a cortex restart.
  2. Change them to 1&2, 4&5, 7&8, the middle one will always give values of -1, 0 or 1

Finally I plug these encoders in port 1&2, 5&6, 7&8, now they are working properly.

The Attached files shows the setup of the robot. I am using the latest robotC 4.30 and updated to the latest cortex firmware.

Is this a bug or feature in robotC or the VEX cortex?


There’s an issue with the cortex involving port 4 and port 10.

See this.
and this.

Try and avoid using port 10 as an output and you should be ok (it’s hard to see your images, they are too small or I would suggest a setup that would work).

Thanks for your prompt reply! I re-posted the images and hope you can now see the images…