我在datasheet看到这样一句话"When configured for SPI (SPI Use = 1 and Comm Modes [1:0] = SPI Master or SPI Slave mode), the input and output direction of pins P1.5, and P1.6 is set automatically by the SPI logic. However, pin P1.4's input and output direction is NOT automatically set; it must be explicitly set by firmware. For SPI Master mode, pin P1.4 must be configured as an output; for SPI Slave mode, pin P1.4 must be configured as an input."