Texas Instruments MSP430x4xx - Manual (Page 186)

Digital I/O Operation
9-3 Digital I/O
9.2 Digital I/O Operation
The digital I/O is configured with user software. The setup and operation of the
digital I/O is discussed in the following sections.
9.2.1 Input Register PxIN
Each bit in each PxIN register reflects the value of the input signal at the
corresponding I/O pin when the pin is configured as I/O function.
Bit = 0: The input is low
Bit = 1: The input is high
Note: Writing to Read-Only Registers PxIN
Writing to these read-only registers results in increased current consumption
while the write attempt is active.
9.2.2 Output Registers PxOUT
Each bit in each PxOUT register is the value to be output on the corresponding
I/O pin when the pin is configured as I/O function and output direction.
Bit = 0: The output is low
Bit = 1: The output is high
9.2.3 Direction Registers PxDIR
Each bit in each PxDIR register selects the direction of the corresponding I/O
pin, regardless of the selected function for the pin. PxDIR bits for I/O pins that
are selected for other module functions must be set as required by the other
function.
Bit = 0: The port pin is switched to input direction
Bit = 1: The port pin is switched to output direction