LEDS EQU P1
TIME EQU 50
LOAD EQU (65536-1000*TIME)

CNT EQU     30h
SEC EQU     31h

ORG 0
    LJMP MAIN

ORG 0BH
    JMP timer_interrupt

ORG 00B0H
main:
    MOV CNT, #20
    MOV SEC, #0
    MOV LEDS, #255
    LCALL delay

m_loop:
    MOV A, SEC
    CPL A
    MOV P1, A
    SJMP m_loop

;--------------------------------------------------
; Function that delays TIME miliseconds
;--------------------------------------------------
delay:
    CLR TR0
    MOV TL0, #LOW(LOAD)
    MOV TH0, #HIGH(LOAD)
    ANL TMOD, #11110000B
    ORL TMOD, #00000001B
    CLR TF0
    SETB ET0
    SETB EA
    SETB TR0
    RET

timer_interrupt:
    MOV TL0, #LOW(LOAD)
    MOV TH0, #HIGH(LOAD)
    DJNZ CNT, return
    MOV CNT, #20
    INC SEC

return:
    RETI
END