There are a total of 12 conversion channels for the ADC12 in the
MSP430. 8-channels (A0 - A7) are dedicated for external signals,
2-channels (A8 and A9) are used to perform conversions on any
external reference voltage used, A10 is used to perform a conversion
on the built-in temperature sensor and A11 is used to perform a
conversion on the voltage level at AVcc. Note that if no external
references are being used, channels A8 and A9 are available to the
user, allowing up to 10 channels for external signals.