你好！
遇到一个比较奇怪的问题。
程序比较简单，用SCI发送一个字符串，串口调试助手总是收不到最后两个字符，用示波器观察，示波器显示的波形跟串口调试助手收到的字符是对应的。但是我看到SCI寄存器的SCITXBUF已经写入了字符串的最后一个字符。
例如，我先定义一个字符串“abcdefg\0”, 用sci 查询发送，没有用FIFO，直到遇到‘\0’。但是串口调试助手只能收到abcde, 但是到最后SCITXBUF里面的是‘g’。
如果发送两个字符串，则第一个字符串里的字节会都收到，但是第二个字符串的最后两个字节会丢失。
实在想不出什么原因。
//=======================================================================================
// FILE: test - main.c
//=======================================================================================
#include "DSP28x_Project.h"
//---------------------------------------------------------------------------------------
// FUNCTION PROTOTYPES
//---------------------------------------------------------------------------------------
void SciaSendByte(char a); // Send a character from the SCI
void SciaSendMsg(char *msg); // Send a string from the SCIA
//---------------------------------------------------------------------------------------
// VARIABLE DECLARATIONS - GENERAL
//---------------------------------------------------------------------------------------
Uint16 ReceivedChar;
char *msg;
//=======================================================================================
// MAIN CODE - starts here
//=======================================================================================
void main(void)
{
DisableDog(); // Disable the watchdog
InitPieCtrl(); // Initializes the PIE control registers to a default state.
IER = 0x0000;
IFR = 0x0000; // Disable CPU interrupts and clear all CPU interrupt flags.
InitPieVectTable(); // Initialize the PIE vector table.
EALLOW;
SysCtrlRegs.PCLKCR0.bit.ADCENCLK = 1; // Enable ADC peripheral clock
(*Device_cal)();
SysCtrlRegs.PCLKCR0.bit.ADCENCLK = 0; // Return ADC clock to original state
EDIS;
InitPll(DSP28_PLLCR, DSP28_DIVSEL); // Initialize the PLL control: PLLCR and CLKINDIV.
EALLOW;
SysCtrlRegs.LOSPCP.all = 0x0002; // low speed clock = SYSCLKOUT/4 22.5MHz@90MHz
SysCtrlRegs.PCLKCR0.bit.SCIAENCLK = 1; // Enable SCI-A clock
EDIS;
EALLOW;
GpioCtrlRegs.GPAMUX2.bit.GPIO28 = 1; // set GPIO28 = SCIRXDA
GpioCtrlRegs.GPAPUD.bit.GPIO28 = 0; // Enable pull-up for GPIO28 (SCIRXDA)
GpioCtrlRegs.GPAQSEL2.bit.GPIO28 = 3; // Asynchronous input GPIO28 (SCIRXDA)
GpioCtrlRegs.GPAMUX2.bit.GPIO29 = 1; // set GPIO29 = SCITXDA
//GpioCtrlRegs.GPAPUD.bit.GPIO29 = 0; // Enable pull-up for GPIO29 (SCITXDA)
GpioCtrlRegs.GPBMUX1.bit.GPIO34 = 0; // set GPIO34 as DE of RS485
GpioCtrlRegs.GPBDIR.bit.GPIO34 = 1; // set GPIO34 output
GpioDataRegs.GPBSET.bit.GPIO34 = 1; // set GPIO34 output high initially(set RS485 send)
EDIS;
// Initiate SCI-A
SciaRegs.SCICCR.all =0x0007; // 1 stop bit, 8 char bits, No parity,
// No loopback, async mode, idle-line protocol
SciaRegs.SCICTL1.all =0x0003; // enable TX, RX, internal SCICLK,
// Disable RX ERR, SLEEP, TXWAKE
SciaRegs.SCIHBAUD =0x0001; // 9600 baud @LSPCLK = 22.5MHz (90 MHz SYSCLK).
SciaRegs.SCILBAUD =0x0024;
SciaRegs.SCICTL1.all =0x0023; // Relinquish SCI from Reset.
SciaSendByte('a');
DELAY_US(5000);
SciaSendByte('b');
SciaSendByte('c');
msg = "\r\nHello World!\0";
SciaSendMsg(msg);
msg = "\r\nYou will enter a character, and the DSP will echo it back!\0";
SciaSendMsg(msg);
//-----------------------------------------------------------------------------------
// MAIN LOOP
//-----------------------------------------------------------------------------------
for(;;) //infinite loop
{
msg = "\r\nEnter: \0";
SciaSendMsg(msg);
//DELAY_US(5000);
//GpioDataRegs.GPBCLEAR.bit.GPIO34 = 1; // set rs485 receive
// Wait to receive a character
while(SciaRegs.SCIRXST.bit.RXRDY == 0)
;
ReceivedChar = SciaRegs.SCIRXBUF.all; // Get the character
//DELAY_US(5000);
//GpioDataRegs.GPBSET.bit.GPIO34 = 1; // set rs485 send
// Echo character back
msg = " You sent: \0";
SciaSendMsg(msg);
SciaSendByte(ReceivedChar);
} // END OF MAIN LOOP
} //END MAIN CODE
// send a character from the SCI-A
void SciaSendByte(char a)
{
while(!(SciaRegs.SCICTL2.bit.TXRDY))
;
SciaRegs.SCITXBUF = a;
}
// send a string from the SCI-A
void SciaSendMsg(char *msg)
{
int i = 0;
while(msg[i] != '\0'){
SciaSendByte(msg[i]);
i++;
}
}
//=======================================================================================
// End of file.
//=======================================================================================
先把程序贴上来，都整到这一个文件里了。
昨天我用的是RS485，在主函数里有一个设置发送和接收（GPIO34），今天先加入了延时（DELAY_US(5000);），发现可以接收到所有字符。换了个板子用
RS232试，就不用加这个延时，因为RS232不用设置发送和接收。
但是无论是RS485还是RS232，我在main函数前用发送单个字符测试，就发送一个字符‘a’，如果不加延时，单步运行就收不到。加了延时，单步运行到延时结束才能收到。不加延时，只有单步运行完SciaSendByte('c');才能收到字符‘a’。
我觉得挺奇怪的。难道我的发送单个字符的函数有问题还是SCI设置有问题？
