Texas Instruments MSP430x1xx manual Function Select Registers PxSEL

Digital I/O Operation

9.2.4Function Select Registers PxSEL

Port pins are often multiplexed with other peripheral module functions. See the device-specific data sheet to determine pin functions. Each PxSEL bit is used to select the pin function − I/O port or peripheral module function.

Bit = 0: I/O Function is selected for the pin

Bit = 1: Peripheral module function is selected for the pin

Setting PxSELx = 1 does not automatically set the pin direction. Other peripheral module functions may require the PxDIRx bits to be configured according to the direction needed for the module function. See the pin schematics in the device-specific datasheet.

;Output ACLK on P2.0 on MSP430F11x1

BIS.B #01h,&P2SEL ; Select ACLK function for pin

BIS.B #01h,&P2DIR ; Set direction to output *Required*

Note: P1 and P2 Interrupts Are Disabled When PxSEL = 1

When any P1SELx or P2SELx bit is set, the corresponding pin’s interrupt function is disabled. Therefore, signals on these pins will not generate P1 or P2 interrupts, regardless of the state of the corresponding P1IE or P2IE bit.

When a port pin is selected as an input to a peripheral, the input signal to the peripheral is a latched representation of the signal at the device pin. While PxSELx=1, the internal input signal follows the signal at the pin. However, if the PxSELx=0, the input to the peripheral maintains the value of the input signal at the device pin before the PxSELx bit was reset.

9-4 Digital I/O