◄Map►                                       ◄Up► ◄Contents► ◄Index► ◄Back►
────────────────────────────────────────────────────────────────────────────
 
;* Sound - Sounds speaker with specified frequency and duration.
;*
;* Shows:   Instructions - in           out
;*
;* Params:  Freq - Desired frequency of sound in Hertz
;*          Duration - Desired duration in clocks, where
;*                     18 clocks = approx 1 second
;*
;* Return:  None
 
Sound   PROC,
        Freq:WORD, Duration:WORD
 
        mov     al, 0B6h                ; Initialize channel 2 of
        out     43h, al                 ;   timer chip
        mov     dx, 12h                 ; Divide 1,193,182 Hertz
        mov     ax, 34DEh               ;   (clock frequency) by
        div     Freq                    ;   desired frequency
                                        ; Result is timer clock count
        out     42h, al                 ; Low byte of count to timer
        mov     al, ah
        out     42h, al                 ; High byte of count to timer
        in      al, 61h                 ; Read value from port 61h
        or      al, 3                   ; Set first two bits
        out     61h, al                 ; Turn speaker on
 
        ; Pause, pass duration of delay
        INVOKE  Pause, Duration
 
        in      al, 61h                 ; Get port value
        xor     al, 3                   ; Kill bits 0-1 to turn
        out     61h, al                 ;   speaker off
        ret
 
Sound   ENDP
                                    -♦-