What could cause pins in a port to change from values I assign to them?

If you are using the port as an output, make sure that you configure it to be as digital port, and not analog port. Some port pins are multiplexed between the ports and other peripherals and so may not be available as I/O if you are using those peripherals.

Check the datasheet for the device you are using for more information on how to set up the ports correctly.

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