MSP430FR6972的串口波特率设置代码

1. 本次使用ACLK，就是辅助时钟（32.768KHZ）作为串口的时钟源，那么使用波特率9600的时候，分频系数=32768/9600=3.41，所以是有小数位的，设置代码如下

  UCA0CTLW0 |= UCSWRST;
  UCA0CTLW0 |= UCSSEL__ACLK;                  // Set ACLK = 32768 as UCBRCLK
  UCA0BR0 = 3;
  UCA0MCTLW |= 0x5300;                      // 32768/9600 - 
  UCA0BR1 = 0;
  UCA0CTL1 &= ~UCSWRST;                     // release from reset

根据TI芯片数据手册提供的资料，小数位是0.41的时候查找最接近的值0.4286，那么UCA0MCTLW |= 0x5300;

同理，如果是4800波特率的话，32768/4800=6.82，提取小数位0.82，最接近的值0XBF，那么代码如下

  UCA0CTLW0 |= UCSWRST;
  UCA0CTLW0 |= UCSSEL__ACLK;                  // Set ACLK = 32768 as UCBRCLK
  UCA0BR0 = 6;
  UCA0MCTLW |= 0xbf00;  
  UCA0BR1 = 0;
  UCA0CTL1 &= ~UCSWRST;                     // release from reset
  UCA0IE |= UCRXIE;