[求助] 求助关于G2内部I2C程序问题

465055608 2012-7-21 17:28 楼主

#include "msp430g2553.h"

unsigned int RxByteCtr;
unsigned int RxWord;

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                // Stop WDT
  P1DIR |= BIT0;                         // P1.0 output
  P1SEL |= BIT6 + BIT7;                   // Assign I2C pins to USCI_B0
  P1SEL2|= BIT6 + BIT7;                   // Assign I2C pins to USCI_B0
  UCB0CTL1 |= UCSWRST;                   // Enable SW reset             I2C复位
  UCB0CTL0 = UCMST + UCMODE_3 + UCSYNC;    // I2C Master, synchronous mode 主设备选择UCMST+I2C UCMODE_3+同步模式UCSYNC
  UCB0CTL1 = UCSSEL_2 + UCSWRST;          // Use SMCLK, keep SW reset    SMCLK+I2C复位
  UCB0BR0 = 12;                            // fSCL = SMCLK/12 = ~100kHz    波特率控制 100kHz
  UCB0BR1 = 0;
  UCB0I2CSA = 0x4e;                      // Set slave address             从设备地址
  UCB0CTL1 &= ~UCSWRST;                   // Clear SW reset, resume operation复位使能禁止
  IE2 |= UCB0RXIE;                         // Enable RX interrupt             接收中断使能
  TACTL = TASSEL_2 + MC_2;                // SMCLK, contmode

  while (1)
  {
RxByteCtr = 2;                         // Load RX byte counter
UCB0CTL1 |= UCTXSTT;                   // I2C start condition             产生START条件
__bis_SR_register(CPUOFF + GIE);       // Enter LPM0, enable interrupts 进入低功耗模式，打开全局中断
                                          // Remain in LPM0 until all data
                                          // is RX'd

if (RxWord < 0x1d00)                   // >28C?
   P1OUT &= ~0x01;                      // No, P1.0 = 0
else
   P1OUT |= 0x01;                      // Yes, P1.0 = 1

__disable_interrupt();
TACCTL0 |= CCIE;                      // TACCR0 interrupt enabled
__bis_SR_register(CPUOFF + GIE);       // Enter LPM0, enable interrupts
                                          // Remain in LPM0 until TACCR0
                                          // interrupt occurs
TACCTL0 &= ~CCIE;                      // TACCR0 interrupt disabled
  }
}

#pragma vector = TIMER0_A0_VECTOR
__interrupt void TA0_ISR(void)
{
  __bic_SR_register_on_exit(CPUOFF);       // Exit LPM0             退出低功耗模式
}

// The USCIAB0TX_ISR is structured such that it can be used to receive any
// 2+ number of bytes by pre-loading RxByteCtr with the byte count.
#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
  RxByteCtr--;                            // Decrement RX byte counter

  if (RxByteCtr)
  {
RxWord = (unsigned int)UCB0RXBUF << 8;  // Get received byte
if (RxByteCtr == 1)                   // Only one byte left?
   UCB0CTL1 |= UCTXSTP;                // Generate I2C stop condition
  }
  else
  {
RxWord |= UCB0RXBUF;                   // Get final received byte,
                                          // Combine MSB and LSB
__bic_SR_register_on_exit(CPUOFF);    // Exit LPM0
  }
}
这是例程1的程序，其中有点不明白，他用定时器0在干吗，有什么作用吗，还有，在while（1）里面，把CCIE开启是干嘛的？他设置了模式2，这个到了0xffff中断就可以了，为什么还要设置CCIE？