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Path: utzoo!utgpu!water!watmath!clyde!rutgers!seismo!mcnc!ecsvax!mjg
From: mjg@ecsvax.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: How do you flush the PC's keyboard?
Message-ID: <3312@ecsvax.UUCP>
Date: Tue, 2-Jun-87 11:22:16 EDT
Article-I.D.: ecsvax.3312
Posted: Tue Jun  2 11:22:16 1987
Date-Received: Thu, 4-Jun-87 05:20:11 EDT
References: <747@thumper.UUCP>
Organization: UNC Educational Computing Service
Lines: 42
Summary: This is how I do it - any better ideas anyone ?

In article <747@thumper.UUCP>, tr@thumper.UUCP writes:
> According to _Advanced MS-DOS_ by Ray Duncan, DOS function C (hex)
> resets the input buffer and then gets a character for input using one
> of five DOS functions.  They are 1, 6, 7, 8, and A (hex).  I want to
> flush the keyboard without getting input.  The reason for this is that
> the next thing my program does is call up a canned function that uses
> keyboard input.
> 

Here is one way to clear the typahead buffer that I
am using successfully in one of my programs.
Since the buffer has been flushed there will not be anything
there but I call function 06 anyway as you MUST specify one
of the functions 1,6,7,8 or A anyway. By using 6 it just checks
the buffer which is empty and returns immediately without waiting.
If by some remote chance a key has been pressed in the split second
etween flushing the buffer and returning then it will be discarded.
by the 06 calls.

----------------------------------------------------
; Clear typeahead buffer routine
; uses flush buffer call, which must specify
; a keyboard command to follow. This method uses
; the int 21h call # 06 which reads the keyboard
; but does not wait for a character

ctahed	proc	near 
	mov     ah,0ch  ;flush keyboard buffer
	mov	al,06   ;function forces a read
	mov     dl,0ffh ;int 21, 06 afterwards.
	int     21h
	jz      nochar  ;
	or      al,al   ;if extended char was typed
	jz      nochar  ;get rid if it by another
	mov     al,6    ;read
	mov	dl,0ffh
	int	21h
nochar: ret
ctahed	endp
----------------------------------------------------

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