After breaking multiple encoder plugs off our NEO encoder wires, our team replaced all of the NEO encoder plugs with REV Data Port Breakout Boards. We have been using the DATA PORT on the Spark Max for the NEO encoder.
The Spark Max User Guide says the DATA PORT can be used for an alternate encoder when the NEO encoder is plugged into the ENCODER PORT. But, can the ENCODER PORT be used for an alternate encoder when the NEO encoder is plugged into the DATA PORT?
No, the pins are physically shared between the encoder pins on the DATA PORT and the pins on the ENCODER PORT, so their only use when in brushless mode is the NEO encoder. For an alternate encoder you will have to use the DATA PORT for it following the pinout guide on our site http://www.revrobotics.com/sparkmax-users-manual/#section-3-6.