I wrote the following code, which is supposed to output a 60 Hz square wave to the PC speaker :

1org 100h
2loop:
3
4	in al, 61h
5	or al, 00000010b ;turn pc speaker on
6	out 61h, al
7	
8	call _wait
9	
10	in al, 61h
11	and al, 11111101b ;turn pc speaker off
12	out 61h, al
13	
14	call _wait
15
16jmp loop
17
18_wait:
19	mov cx, 00h
20	mov dx, 411ah ;wait 16.666ms
21	mov ah, 86h
22	int 15h
23	ret

It can be compiled under NASM (http://www.nasm.us/) using the following command :

1nasm sound.asm -o sound.com

The PC speaker is turned on/off using bit 1, as described here : http://wiki.osdev.org/PC_Speaker#The_Raw_Hardware

However, when run under DOSBOX it does not works as expected (I did not try on real hardware) :
- It only output sound for a short time, then silence. Why ?
- The sound is heavily distorted. It does not sounds at all like a 100% perfect square wave.
How can I fix this ?

Important : as stated in the OSDev page, the PC Speaker can be controlled using the PIT. However this is not what i want. I want to control the PC speaker directly by sending one and zeroes (in order to output something different than a square wave).