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From: farren@hoptoad.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Turning on sound and keyboard info.
Message-ID: <1872@hoptoad.uucp>
Date: Thu, 26-Feb-87 20:24:14 EST
Article-I.D.: hoptoad.1872
Posted: Thu Feb 26 20:24:14 1987
Date-Received: Sat, 28-Feb-87 08:12:09 EST
References: <262@crys.WISC.EDU> <2617@jade.BERKELEY.EDU>
Reply-To: farren@hoptoad.UUCP (Mike Farren)
Distribution: comp
Organization: Nebula Consultants in San Francisco
Lines: 37
Keywords: sound, keyboard

The question was asked: how to put out a sound which will then run without
processor intervention.  On a standard IBM PC, this is done by placing a
divisor value into one of the timer registers, and then enabling the speaker.
Once you do this, the speaker will be toggled every time the timer overflows,
and the timer will be reset to do the whole process over again.  This continues
until you explicitly turn off the speaker.  Sample assembly code (not tested)
for this operation is as follows:

;This routine turns on the speaker with a tone whose frequency is
  ((1/1193180) * divisor) hertz

onspeaker:
    mov    al, 0B6h   ;select timer 2
    out    043h, al   ;Send to mode register in timer
    mov    ax, divisor ;Select frequency
    out    042h, al   ;Send LSB of divisor to timer
    mov    al, ah
    out    042h, al   ;Send MSB of divisor to timer
    in     al, 061h   ;Get current contents of control port
    mov    byte ptr save_mode, al  ; Save current contents somewhere
    or     al, 03h    ;Set bits to turn on speaker
    out    061h, al   ;And do it


; This routine turns off the speaker

offspeaker:
    mov    al, byte ptr save_mode  ;Get the old contents
    out    061h, al   ;Turn the speaker off

Hope this helps some.

-- 
----------------
                 "... if the church put in half the time on covetousness
Mike Farren      that it does on lust, this would be a better world ..."
hoptoad!farren       Garrison Keillor, "Lake Wobegon Days"