EEPW论坛

问 请教一下一个标称 4M Hz 的晶振它的值是 4000000 Hz 还是4×1024×1024 Hz？:confused: 答 1: 是前者，比如32KHZ的都是标注32.768。如果是4*1024*1024上面会标注：4.194304MHZ。 答 2: 可是无论我用4MHz还是4.194304MHz作UATR的波特率时钟，产生4800波特率都能正确发送数据。我想可能是在它的误差范围内，对吗？ 答 3: 是的。通常串行每位的误差允许在20%以内。 答 4: 但是我发现接收时误码很高几乎是50％出错或根本接收不到，不知是什么原因？我的代码很简单就是设置接收中断

#include <MSP430x12x.h>

void main(void)
{
unsigned int i;
/**/
unsigned char send[34] = {0x61,0x62,0x63,0x64,0x61,0x62,0x63,0x64
,0x61,0x62,0x63,0x64,0x61,0x62,0x63,0x64
,0x61,0x62,0x63,0x64,0x61,0x62,0x63,0x64
,0x61,0x62,0x63,0x64,0x61,0x62,0x63,0x64
,0x61,0x62};
/**/

WDTCTL = WDTPW + WDTHOLD; // Stop WDT
BCSCTL1 |= XTS; // ACLK = LFXT1 = HF XTAL

do
{
IFG1 &= ~OFIFG; // Clear OSCFault flag
for (i = 0xFF; i > 0; i--); // Time for flag to set
}
while ((IFG1 & OFIFG) != 0); // OSCFault flag still set?

BCSCTL2 |= SELM1+SELM0; // MCLK = LFXT1 (safe)
UCTL0 = CHAR; // 8-bit character
UTCTL0 = SSEL0; // UCLK = ACLK

UBR00 = 0x41; // 4Mhz/4800 - 833
UBR10 = 0x03; //
UMCTL0 = 0x44; //

ME2 |= UTXE0 + URXE0; // Enabled USART0 TXD/RXD
IE2 |= URXIE0; // Enabled USART0 RX interrupt
P3SEL |= 0x30; // P3.4,5 = USART0 TXD/RXD
P3DIR |= 0x10; // P3.4 output direction
_EINT(); // Enable interrupts

for (;;)
{
/**发送正常
for(i=0;i<34;i++)
{
while((IFG2 & UTXIFG0) == 0)
TXBUF0 = send[i];
}
**/
/**/
_BIS_SR(LMP3);
_NOP(); // Required only for C-spy
/**/
}
}

interrupt[UART0RX_VECTOR] void usart0_rx (void)
{
while ((IFG2 & UTXIFG0) == 0); // USART0 TX buffer ready?
TXBUF0 = RXBUF0; // RXBUF0 to TXBUF0
}