.model small
.stack 100h

.data
    hours db ?
    minutes db ?
    seconds db ?

.code
    ; Main program entry point
    main proc
        mov ax, @data
        mov ds, ax

        ; Prompt the user to enter the starting time
        mov ah, 09h
        mov dx, offset start_prompt
        int 21h

        ; Read the starting time from the user
        mov ah, 01h
        int 21h
        sub al, 48       ; Convert ASCII value to decimal
        mov hours, al

        ; Initialize the minutes and seconds
        mov minutes, 0
        mov seconds, 6   ; Set initial seconds to the user input

        ; Display the clock
        display_clock:
        mov ah, 02h
        mov dl, '0'      ; Print leading zero for hours
        int 21h
        mov dl, hours
        add dl, 48       ; Convert decimal value to ASCII
        int 21h

        mov dl, ':'
        int 21h

        mov dl, '0'      ; Print leading zero for minutes
        int 21h
        mov dl, minutes
        add dl, 48       ; Convert decimal value to ASCII
        int 21h

        mov dl, ':'
        int 21h

        mov dl, '0'      ; Print leading zero for seconds
        int 21h
        mov dl, seconds
        add dl, 48       ; Convert decimal value to ASCII
        int 21h

        ; Increment the seconds
        increment_seconds:
        inc seconds

        ; Check if the seconds reach 60
        cmp seconds, 60
        jl update_clock

        ; Reset seconds to 0
        mov seconds, 0

        ; Increment the minutes
        increment_minutes:
        inc minutes

        ; Check if the minutes reach 60
        cmp minutes, 60
        jl update_clock

        ; Reset minutes to 0
        mov minutes, 0

        ; Increment the hours
        increment_hours:
        inc hours

        ; Check if the hours reach 12
        cmp hours, 12
        jl update_clock

        ; Reset hours to 0
        mov hours, 0

        ; Reset the clock to 00:00:00 after 11:59:59
        reset_clock:
        cmp hours, 0
        jne display_clock

        cmp minutes, 0
        jne display_clock

        cmp seconds, 0
        jne display_clock

        ; Return to DOS
        mov ah, 4Ch
        mov al, 0
        int 21h

    main endp

    start_prompt db 0Ah, "Enter the starting time (0-9): $"

end main