how cain pass through a pointer's address to a function

First, code is easier to read on this forum if you use the &ltpre&gt and &lt/pre&gt tags (see the "Tips for Posting Messages" link in the side bar) - like this:

#include <reg51.h>

#define record 7

#define byte  unsigned char
#define word  unsigned int
#define dword unsigned long int

//declare funtions
void save_block( byte xdata *start_addr, word xdata *chksum );
word calc_block( byte xdata *start_addr, word xdata *chksum );
bit  chk_block(  byte xdata *start_addr, word xdata *chksum );

//declare variables
xdata byte par_buff1[14];
xdata word chksum1;

xdata byte dummy1;

xdata byte xdata *rec_buf_start;
xdata byte xdata *rec_buf_end;
xdata byte xdata *wr_ptr;
xdata byte xdata *rd_ptr;
xdata word chksum2;

xdata word xdata **valami;

main()
{
    //valami=&rec_buf_start;
    if(chk_block(&rec_buf_start,&chksum2))
    {
        // do something
    }
    if(chk_block(&par_buff1[0],&chksum1))
    {
        //do something
    }
    else
    {
        //do something
    }
    for(;;)
    {
        //do something 
    }
} 
etc

if(chk_block&rec_buf_start,&chksum2))

if(chk_block( &rec_buf_start, &chksum2 ))

bit chk_block( byte xdata *start_addr, word xdata *chksum );

xdata byte xdata *rec_buf_start;

thanks for Your answer

I understand your explanation, but I would like to a calculate pointers controlsum not that place where pointers point to. I can do it if I declare a new dummy byte(U8) variable before the line where my first pointer placed.

//declare
xdata byte dummy;
xdata byte xdata *rec_buf_start;
xdata byte xdata *rec_buf_end;
xdata byte xdata *rd_ptr;
xdata byte xdata *wr_ptr;
xdata word chksum1;

main()
 {
 *chksum1=calc_chk(&dummy, &chksum1);
 }

You are not guaranteed to have these variables in order in memory (ANSI C). You can force this be selecting "Keep variables in order" I think but this is a weak thing to do. It's too fragile and will break easily. Put your pointers into a struct like this:

typedef unsigned char  U8;
typedef unsigned short U16;


typedef struct {
    // All pointers to XDATA only.
    U8 * xdata rec_buf_start;
    U8 * xdata rec_buf_end;
    U8 * xdata rd_ptr;
    U8 * xdata wr_ptr;
} Pointer;

int main(void)
{
    // Put struct into XDATA too.
    Pointer xdata ptrs;
    U16 idata chksum;

    chksum = calcChecksum(&ptrs);

    return 0;
}

So, you want to treat the pointers as just ordinary numbers, and calculate a checksum on those numbers?

Can't you just use a cast?

Yes I'd like to do that, but I don't know how do I do it. I program always in assembly and nowadays i'd like to apply C language in my job. It's not to easy change my assembly oriented attitud.
So I should greatly appreciate if You show it the good solution.

thank in advance Leslie

unsigned char *Ptr;
unsigned long  PtrVal;

    Ptr = &something;
    PtrVal = (unsigned long)Ptr;