基于CC2430/31的Zigbee实践（6）--波特率计算方法

1、波特率计算方法
在UART和SPI两种模式下，波特率都是由一个CC2430内在的波特率发生器产生，UxBAUD.BAUD_M[7:0]和UxGCR.BAUD_E[4:0]寄存器分别记录了转换的尾数和指数，公式如下：
Buadrate=（256+Baud_M）*（2的Baud_E次方）*F/（2的28次方）
       其中F为系统的时钟频率=16MHz或者32MHz。The maximum baud rate for UART mode is F/16 when BAUD_E is 16 and BAUD_M is 0, and where F is the system clock  requency. The maximum baud rate for SPI mode and thus SCK frequency, is F/2 when BAUD_E is 19 and BAUD_M is 0. Setting higher baud rates than this will give erroneous results。
Baud rate (bps)                UxBAUD.BAUD_M              UxGCR.BAUD_E                  Error (%)
2400                                           59                                       6                                0.14
4800                                           59                                       7                                0.14
9600                                           59                                       8                                0.14
14400                                         216                                     8                                0.03
19200                                         59                                       9                                0.14
28800                                         216                                     9                                0.03
38400                                         59                                       10                              0.14
57600                                         216                                     10                              0.03
76800                                         59                                       11                              0.14
115200                                       216                                     11                              0.03
230400                                       216                                     12                              0.03
                                Commonly used baud rate settings for 32 MHz system clock

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