using 2nd DPTR in DS87C520

Hi
I want to use the second data pointer available in Dallas, since i am reading my port and then immediatly writing this data to external ram.All this has to be done in ISR in 10us. I am using in line assembly but the code is not working when i use both data pointers.

void external0(void) interrupt 0 using 1
{

//TRACK1[LEN_TRK1++]=XBYTE[0x8000]; //TRACK1[LEN_TRK1++] = XBYTE[0x8001];

//The above two C statements are replaced by the below mentioned Assembly code

#pragma ASM
SETB DPS ; DPS=1 ACTIVE DPTR1
MOV DPTR,#08000H
MOVX A,@DPTR ; READ
INC DPTR

CLR DPS ; DPS=0 ACTIVE DPTR0
MOV DPL,LEN_TRK1+01H
MOV DPH,LEN_TRK1
MOVX @DPTR,A ; WRITE
INC DPTR

SETB DPS ; DPS=1 ACTIVE DPTR1
MOVX A,@DPTR ; READ
CLR DPS ; DPS=0 ACTIVE DPTR0
MOVX @DPTR,A ; WRITE
INC DPTR
MOV LEN_TRK1+01H,DPL
MOV LEN_TRK1,DPH
#pragma ENDASM
}

Thanx
Faisal