PIN的设置

     虽然做过几个项目，但对单片机PIN的设置一直不是很明白，前几天安装了silabs IDE的3.2，有很多例子。下面这个对此做了比较详细的说明。

P0.7与P3.3都是digital，所以P0MDOUT及P3MDOUT可以对相应的PIN做设置。

//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This function configures the crossbar and ports pins.
//
// To configure a pin as a digital input, the pin is configured as digital
// and open-drain and the port latch should be set to a '1'.  The weak-pullups
// are used to pull the pins high.  Pressing the switch pulls the pins low.
//
// To configure a pin as a digital output, the pin is configured as digital
// and push-pull. 
//
// An output pin can also be configured to be an open-drain output if system
// requires it.  For example, if the pin is an output on a multi-device bus,
// it will probably be configured as an open-drain output instead of a
// push-pull output.  For the purposes of this example, the pin is configured
// as push-pull output because the pin in only connected to an LED.
//
// P0.7   digital   open-drain    Switch 1
// P3.3   digital   push-pull     LED1
//-----------------------------------------------------------------------------
void PORT_Init (void)
{
   P0MDIN |= 0x80;                     // P0.7 is digital
   P3MDIN |= 0x08;                     // P3.3 is digital

   P0MDOUT = 0x00;                     // P0.7 is open-drain
   P3MDOUT = 0x08;                     // P3.3 is push-pull

   P0     |= 0x80;                     // Set P0.7 latch to '1'

   XBR1    = 0x40;                     // Enable crossbar and enable
                                       // weak pull-ups
}