Uart using mode 3

Yes, it is very often the case that the "easy" option is the most limited option - and working around those limitations can soon make the "hard" option a lot simpler!

In this case, I don't think polled transmission should be difficult - reception is another thing...

Yes, it is very often the case that the "easy" option is the most limited option - and working around those limitations can soon make the "hard" option a lot simpler!

In this case, I don't think polled transmission should be difficult - reception is another thing...

I tried to change the codes to check Tx interrupt flag before using serial buffer register(SFR : SBUF_0, SBUF_1).

the result is uart1 has totally no respond(uart0 still works), but when I use uart0 after I check uart1 doesn't work, I see uart1 prints test string("==Exciter Uart1 Test==") just once through hyper-terminal(I use two hyper terminal program, for uart0 and uart1). the condition is when I use uart0 just after checking uart1 does not work, then I see this phenomenon.

void print_Uart0(char *sBuf_0)
{
    while(*sBuf_0 != NULL)
    {
        while(!TI_0);<== add this
        TI_0 = 0;  <== add this
        SBUF_0 = *sBuf_0++;
    }
    while(!TI_0);<== add this
    TI_0 = 0;><== add this
    SBUF_0 = 0x0D;
}

void print_Uart1(char *sBuf_1)
{
    while(*sBuf_1 != NULL)
    {
        while(!TI_1);<== add this
        TI_1 = 0;  <== add this
        SBUF_1 = *sBuf_1++;
    }
    while(!TI_1);<== add this
    TI_1 = 0;><== add this
    SBUF_1 = 0x0D;
}

and add this codes in initial of main function

 TI_0 = 1;
 TI_1 = 1;
 RI_0 = 0;
 RI_1 = 0;

I tried codes below, and saw both uarts(uart0/uart1) were working concurrently.
I just made reset each tx interrupt flag(TI_0/TI_1) in different place.

#include <stdio.h>
#include <string.h>
#include "at89c51re2_2.h"
#include "INTRINS.H"

#define TRUE              1
#define FALSE             0
#define BUF_SIZE          50

typedef unsigned char       Int8;
typedef signed char         SignedInt8;
typedef unsigned short      Int16;
typedef signed short        SignedInt16;
typedef unsigned long       Int32;
typedef signed long         SignedInt32;
typedef bit                 Boolean;

Int8        serialBuf[BUF_SIZE];
Int8        serialBufPos;
Int8        serialByte;
Boolean     parseCommandFlag = FALSE;

Int8        serialBuf1[BUF_SIZE];
Int8        serialBufPos1;
Int8        serialByte1;
Boolean     parseCommandFlag1 = FALSE;

void print_Uart0(char *sBuf_0)
{
    while(*sBuf_0 != NULL)
    {
        SBUF_0 = *sBuf_0++;
    }
    SBUF_0 = 0x0D;
}

void print_Uart1(char *sBuf_1)
{
    while(*sBuf_1 != NULL)
    {
        while(!TI_1);
        TI_1 = 0;
        SBUF_1 = *sBuf_1++;
    }
    while(!TI_1);
    TI_1 = 0;
    SBUF_1 = 0x0D;
}

void ParseCommand (void)
{
    print_Uart0("\n==Exciter UART0 Test==\n");
    memset(serialBuf, 0x00, sizeof(Int8)*BUF_SIZE);
    serialBufPos = 0;
    parseCommandFlag = FALSE;
}

void ParseCommand1(void)
{
    print_Uart1("\n==Exciter UART1 Test==\n");
    memset(serialBuf1, 0x00, sizeof(Int8)*BUF_SIZE);
    serialBufPos1 = 0;
    parseCommandFlag1 = FALSE;
}

void main (void)
{
    memset(serialBuf, 0x00, sizeof(Int8)*BUF_SIZE);
    serialBufPos = 0;
    memset(serialBuf1, 0x00, sizeof(Int8)*BUF_SIZE);
    serialBufPos1 = 0;

/********* Timer Set ********/
    T2CON = 0;
    BDRCON_0 |= 0x0C; //RBCK_0 = 1, TBCK_0 = 1
    BDRCON_1 &= 0xF3; //RBCK_1 = 0, TBCK_1 = 0

    TMOD |= 0x20 ;         /* Timer 1 in mode 2 */

/****** UART0 ******/
    //use internal Baud Rate Generator
    SCON_0 = 0x50;    /* uart0 in mode 1 (8 bit), REN_0=1 */
    BDRCON_0 &=0xEC;  /* BRR_0=0; SRC_0=0; SPD_0 = 0*/
    PCON |= 0x80;     /* SMOD1_0 = 1;*/
    BRL_0 = 251;      /* set 19200, @18.432Mhz (BRL_0=251;SPD_0=1;SMOD1_0=0) */


/****** UART1 ******/
    SCON_1 = 0x50;    /* uart1 in mode 1 (8 bit), REN_1=1*/
    BDRCON_1 |= 0x80;
    TH1  = 0xFB;                 /* 19200 Bds at 18.432MHz */

    TI_0 = 1;
    TI_1 = 1;
    RI_0 = 0;
    RI_1 = 0;

    IEN1 |= 0x08;    /* Enable serial port1 interrupt   */
    ES = 1;          /* Enable serial port0 interrupt   */
    EA = 1;              /* Enable global interrupt */

    BDRCON_0 |=0x10; /* Baud rate generator run*/
    TR1 = 1;
    while(1)
    {
        if(parseCommandFlag == TRUE)
            ParseCommand();
        if(parseCommandFlag1 == TRUE)
            ParseCommand1();
    }
}

void serial0_IT(void) interrupt 4
{
    if (RI_0 == 1)
    {
        RI_0 = 0;

        serialByte = SBUF_0; /* Read receive data */
        if (serialByte == ' ')
        {
            /* skip space */
        }
        else if (serialByte == 0x0D)    /* CR */
        {
            serialBuf [serialBufPos] = '\0';
            parseCommandFlag = TRUE;
        }
        else
        {
            if ((serialByte >= 'a') && (serialByte <= 'z'))
            {
                serialByte -= 0x20;     /* 0x20 = 'a' - 'A' */
            }
            serialBuf [serialBufPos] = serialByte;
            serialBufPos++;
        }
    }
    else if (TI_0 == 1)
        TI_0 = 0;
}

void serial1_IT(void) interrupt 10
{
    if (RI_1 == 1)
    {
        RI_1 = 0;

        serialByte1 = SBUF_1; /* Read receive data */
        if (serialByte1 == ' ')
        {
            /* skip space */
        }
        else if (serialByte1 == 0x0D)    /* CR */
        {
            serialBuf1[serialBufPos1] = '\0';
            parseCommandFlag1 = TRUE;
        }
        else
        {
            if ((serialByte1 >= 'a') && (serialByte1 <= 'z'))
            {
                serialByte1 -= 0x20;     /* 0x20 = 'a' - 'A' */
            }
            serialBuf1[serialBufPos1] = serialByte1;
            serialBufPos1++;
        }
    }
}