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