thank you Mr karas
I was revising my program. but i want to back to my first question. If 1 second, mcs 51 take 1 milion instruction ( crystal 12Mhz ). what could happened with this program :

MOV P0,#00H
MOV R0,#21H
START_IN:
MOV A,#001
CON_IN :
MOV C,P0.0
RLC A
JNC CON_IN
CJNE A,#00H,DATA_IN ;TO AVOID DATA =00H
CJNE R0,#21H,DATA_IN ; IN FIRST RAM
JMP CON_IN
DATA_IN :
MOV @R0,A
INC R0
CJNE R0,#07FH,START_IN ; TO AVOID STACK OVER FLOW
RET

If i am connecting P0.0 for 2 second, will the memory full of data.
what can i do to save more of data, decrement crystal frequency or use external memory

best regard