下面这两句话是什么意思？请明白的朋友解释一下，先谢过了~
For the device family, pin multiplexing can be controlled on a pin-by-pin basis. Each pin that is multiplexed
with several different functions has a corresponding 4-bit field in one of the PINMUX registers.
Pin multiplexing selects which of several peripheral pin functions controls the pin's IO buffer output data
and output enable values only. The default pin multiplexing control for almost every pin is to select 'none'
of the peripheral functions in which case the pin's IO buffer is held tri-stated.