Mr Erik, you are right. but in my complete program is like below :

ORG 0H
MOV R0,#21H
MOV P0,#00H
MOV P1,#00H
AJMP START
;******************************************************
INPUT : MOV SP,#20H ; First Stack
START_IN : MOV R2,#08H
MOV ACC,#00H
CON_IN : MOV C,P0.0
MOV ACC.0,C
MOV B,ACC
RL A
DJNZ R2,CON_IN
MOV ACC,B
CJNE A,#00H,DATA_IN
MOV ACC,SP
CJNE A,#20H,SAMPLING
JMP START_IN
DATA_IN : MOV ACC,B
PUSH ACC
JMP START_IN
;******************************************************
SAMPLING :

i don't think So, cause when i compare it with 00h then if ACC = 00h it will see the SP otherwise if SP = 20H ( first stack ) it jump to START_IN. So if ACC = 00H, it never be PUSH.

best regard
Giri.