Dioda-Timer

org 00H
JMP start

org 03H
JMP switch

org 1BH
JMP full

full:
    INC R3
    MOV TL1, #0
    MOV TH1, #0
    ANL TCON, #01111111b
    RETI

switch:
    MOV R3, #0
    MOV TMOD, #00010000b
    MOV TCON, #01000000b

    loop:
        MOV A, R3
        CJNE A, #5, loop

    JB P3.2, return

    CPL P3.4
    MOV TCON, #0
    MOV TMOD, #0
    MOV TL1, #0
    MOV TH1, #0

    return:
        RETI

start:
    MOV IE, #10000001b
    SETB IP.3
    sjmp $

end