ORG 00H
    JMP START
    ORG 0BH
    JMP TIMER0_INT
START:  MOV SP,#30H
    MOV IE,#10000010B
    MOV TMOD,#00000001B
    MOV R0,#20
    MOV R1,#00H
    MOV P1,#00H
    MOV TH0,#>(65536-50000)
    MOV TL0,#<(65536-50000)
    SETB TR0
    JMP $

TIMER0_INT:
    DJNZ R0,NOT_1S
    MOV R0,#20
    MOV A,R1
    ADD A,#01H
    DA A
    MOV R1,A
    SWAP A
    MOV P1,A
NOT_1S: MOV TH0,#>(65536-50000)
    MOV TL0,#<(65536-50000)
    RETI
    END