如果是STC89C51 STC89C52的话，可以用定时器2做串口波特率发生器，#include "reg51.h"
#include "intrins.h"


sfr T2CON  = 0xC8;          //timer2 control register
sfr RCAP2L = 0xCA;
sfr RCAP2H = 0xCB;
sfr TL2    = 0xCC;
sfr TH2    = 0xCD;


typedef unsigned char BYTE;
typedef unsigned int WORD;


#define FOSC 11059200L      //System frequency
#define BAUD 115200       //UART baudrate


/*Define UART parity mode*/
#define NONE_PARITY     0   //None parity
#define ODD_PARITY      1   //Odd parity
#define EVEN_PARITY     2   //Even parity
#define MARK_PARITY     3   //Mark parity
#define SPACE_PARITY    4   //Space parity


#define PARITYBIT EVEN_PARITY   //Testing even parity


sbit bit9 = P2^2;           //P2.2 show UART data bit9
bit busy;


void SendData(BYTE dat);
void SendString(char *s);


void main()
{
#if (PARITYBIT == NONE_PARITY)
    SCON = 0x50;            //8-bit variable UART
#elif (PARITYBIT == ODD_PARITY) || (PARITYBIT == EVEN_PARITY) || (PARITYBIT == MARK_PARITY)
    SCON = 0xda;            //9-bit variable UART, parity bit initial to 1
#elif (PARITYBIT == SPACE_PARITY)
    SCON = 0xd2;            //9-bit variable UART, parity bit initial to 0
#endif


    TL2 = RCAP2L = (65536-(FOSC/32/BAUD)); //Set auto-reload vaule
    TH2 = RCAP2H = (65536-(FOSC/32/BAUD)) >> 8;
    T2CON = 0x34;           //Timer2 start run
    ES = 1;                 //Enable UART interrupt
    EA = 1;                 //Open master interrupt switch


    SendString("STC89-90xx Uart Test ! ");
    while(1);
}


/*----------------------------
UART interrupt service routine
----------------------------*/
void Uart_Isr() interrupt 4
{
    if (RI)
    {
        RI = 0;             //Clear receive interrupt flag
        P0 = SBUF;          //P0 show UART data
        bit9 = RB8;         //P2.2 show parity bit
    }
    if (TI)
    {
        TI = 0;             //Clear transmit interrupt flag
        busy = 0;           //Clear transmit busy flag
    }
}


/*----------------------------
Send a byte data to UART
Input: dat (data to be sent)
Output:None
----------------------------*/
void SendData(BYTE dat)
{
    while (busy);           //Wait for the completion of the previous data is sent
    ACC = dat;              //Calculate the even parity bit P (PSW.0)
    if (P)                  //Set the parity bit according to P
    {
#if (PARITYBIT == ODD_PARITY)
        TB8 = 0;            //Set parity bit to 0
#elif (PARITYBIT == EVEN_PARITY)
        TB8 = 1;            //Set parity bit to 1
#endif
    }
    else
    {
#if (PARITYBIT == ODD_PARITY)
        TB8 = 1;            //Set parity bit to 1
#elif (PARITYBIT == EVEN_PARITY)
        TB8 = 0;            //Set parity bit to 0
#endif
    }
    busy = 1;
    SBUF = ACC;             //Send data to UART buffer
}


/*----------------------------
Send a string to UART
Input: s (address of string)
Output:None
----------------------------*/
void SendString(char *s)
{
    while (*s)              //Check the end of the string
    {
        SendData(*s++);     //Send current char and increment string ptr
    }
}