如何设置波特率使误差最小

只看该作者 · 2020-9-22 20:03

如何设置波特率使误差最小?

只看该作者 · 2020-9-22 20:13

EXAMPLE: a baud rate of 4800 baud is required with a crystal frequency of
32,768 Hz. This is necessary because the UART also has to run during low power
mode 3. With only the ACLK available, the theoretical division factor—the
truncated value is the content of baud-rate register UBR (UBR1/UBR0)—is:
UBR
32768
4800
6.82667

只看该作者 · 2020-9-22 20:13

还有相应的函数：
void SetBaudRateRegisters(long clk,long baud)
{
int n = clk / baud;    //整数波特率
char mSum = 0;          //Σmi
int txEr0;             //对应位为0时错误率
int txEr1;             //对应位为1时错误率
char i = 0;          //循环计数

UxBR1 = n >> 8;       //高8位
UxBR0 = n & 0xff;    //低8位
UxMCTL = 0;

//循环比较错误率大小设置UxMCTL
for(;i < 8;i++)
{
      txEr0 = 100 * baud * ((i + 1) * n + mSum) / clk - 100 * (i + 1);
      txEr1 = 100 * baud * ((i + 1) * n + mSum + 1) / clk - 100 * (i + 1);
      if(abs(txEr1) < abs(txEr0))
      {
         mSum++;
         UxMCTL |= (1<<i);
      }
}
}