PORT PROBLEM!!!!

Hi everyone.....
Hope u r fine.......
I have a problem in the following code

ORG 00H
BACK:MOV A,#55H
MOV P1,A
ACALL DELAY
MOV A,#0AAH
MOV P1,A
ACALL DELAY
SJMP BACK
DELAY:
MOV R3,#70
H2:MOV R4,#254
H1:DJNZ R4,H1
DJNZ R3,H2
RET
END

Now if i see the output in port P1
I see that
P1:0xAA then 0X55 then 0XAA then 0x55 (repeat continuously......)toggling
Pins:0xAA then 0X55 then 0XAA then 0x55 (repeat continuously......)toggling
Now if i modify my program by just replacing
port P1 by port P0 in all lines
and now if i see output in port P0
i see that..
P1:0xAA then 0X55 then 0XAA then 0X55 (repeat continuously......)toggling
pins:there is no change or toggling
Why is it so??????
Why is there no toggling in output window of port p0 under pins:
pins:No change
P0:toggling
plz help me out......