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90 lines
3.1 KiB
NASM
90 lines
3.1 KiB
NASM
4 years ago
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; It will play 12 notes of the octave starting at middle C.
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;-----------------------------------------------------------------------------
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; How to generate sound on the IBM PC :
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;
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; The 8255 (port 61H) bit 0 controls the 8253 timer
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; bit 1 controls the speaker
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;
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; The output channel 2 from the 8253 timer will be ANDed with the
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; speaker control bit in order to turn on/off the speaker.
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;
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; Timer channel 2 internal count register (port 42h) is loaded in
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; two successive OUT operations with the lower byte being loaded first.
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; For this to work properly, timer command register has to be loaded first
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; with B6H.
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;
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; Since the input clock to the timer chip is 1.19318 MHz, the counter value
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; to generate the frequency X can be calculated by 1193180 / X.
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;-----------------------------------------------------------------------------
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; CX is used as a note counter with the frequency effectively being
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; incremented by a half tone and the corresponding count being loaded
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; into the count register on each iteration.
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;
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; No stack segment is needed for this small program, so don't panic
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; when you receive the 'No stack segment' warning.
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;
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; Arne Asplem 880731 (MASM 4.0)
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dseg segment ; data segment
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notes dw 262,277,294,311,330,349,370,392,415,440,466,494
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dseg ends
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cseg segment
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sound proc far
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assume cs:cseg, ds:dseg, ss:nothing
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start:
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mov ax, dseg
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mov ds, ax ; set up data segment (DS) reg.
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xor si, si
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mov bx, 12 ; note count
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; set up timer command register and counter register
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mov al, 0b6h ; set 8253 command register
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out 43h, al ; for channel 2, mode 3
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nloop:
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mov ax, 34dch ; low part of clock freq.
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mov dx, 12h ; hight part of clock freq.
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div [notes + si] ; get note from data segment
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out 42h, al ; 8253 command register (low byte)
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mov al, ah
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out 42h, al ; 8253 command regsieter (high byte)
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; turn on low bits in 8255 output port
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in al, 61h ; read current value of 8255 port
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or al, 3 ; clear low bits
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out 61h, al ; send new value to port
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; loop while note is sounding
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mov cx, 6d60h
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rpta:
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loop rpta ; 1/10 sec delay
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; turn off speaker, check note count, set up next note
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xor al, 3
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out 61h, al ; turn off speaker
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mov cx, 0af0h
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rptb:
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loop rptb ; 1/100 sec delay
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inc si ; increment note pointer
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inc si
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dec bx ; decrement note counter
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jnz nloop ; loop until bx = 0
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mov ax, 4c00h ; terminate program
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int 21h
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sound endp
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cseg ends
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end start
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