need meaning full details for start up code of lpc2148

So start here:

http://www.keil.com/books
http://www.keil.com/support/man_arm.htm

In particular, http://www.keil.com/support/man/docs/gsac/

startup.o(.text+0x12c):/cygdrive/f/CHECK/check_uart/Startup.s:256: undefined reference to '_start'

startup.o(.text+0x140):/cygdrive/f/CHECK/check_uart/Startup.s:256: undefined reference to '_data'

I guess that, you are using GNU startup code of lpc2148 on KEIL environment; this is incorrect. KEIL has its own startup code of lpc2148.

while creating the target ..... compiler asking to add start up code of lpc2148...... i am using that start up code........still i am in trouble.... if i want to add lpc2148 start up code..... where i get this code and how do i add......

=> still i am in trouble <=

What kind of trouble?

Where did you get the source code?

its my own code for lpc2148 uart
i am sending my code........

#include <LPC21xx.H>

typedef unsigned char U8;
typedef unsigned int U16;
typedef unsigned long int U32;

void uartInit();
void serialTrans(U8);




void main()
{
        //VPBDIV = 0X02;
        uartInit();
        serialTrans( 's' );



while(1);
}

void serialTrans( U8 put )
{
        U1THR = put;
        while(!(U1LSR & 0X20));
        U1LSR &= 0XDF;
}

void uartInit()
{
        PINSEL0 |= 0X00050000;
        U1LCR   = 0X80;
        U1DLL   = 0X5D;
        U1DLM   = 0X00;
        U1LCR   = 0X03;
}

If this is the case, then I think that you should follow Andy's advice first.

See this:

http://www.keil.com/support/man/docs/gsac/gsac_createapps.htm

One more thing, do you have your own LPC21xx.H?

In your case, you should have only two files, one is your code, another is KEIL's startup code.