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From: thj@hpcnof.UUCP (Thomas Hjellming)
Newsgroups: net.micro.pc
Subject: Re: Return codes from resident routines on INT 16H
Message-ID: <960004@hpcnof.UUCP>
Date: Fri, 5-Sep-86 16:06:42 EDT
Article-I.D.: hpcnof.960004
Posted: Fri Sep  5 16:06:42 1986
Date-Received: Sun, 7-Sep-86 05:51:06 EDT
References: <458@bucsb.bu.edu.UUCP>
Organization: HP Colorado Networks Division
Lines: 54


>  what should a resident routine that
>intercepts INT 16H return for registers and flags?  I want to make it seem
>that no key had been pressed.

    Jim,

      You can find this information in Peter Norton's 'Programmers Guide
to the IBM PC'.  I will summarize the info here.

     The subfunctions under Int 16h are:

  AH input value          Register outputs             Description

       0                   AH = scan code        Inputs the next character
                          (auxiliary byte)       from the keyboard.  If one
                                                 is not available, control is
                           AL = character code   not returned until a key is
                          (main byte)            pressed.

       1                   ZF = 0 if key is      Check to see if a key has
                             available, else 1.  been pressed.  NOTE:  if
                           AH and AL are set     a key has been pressed, you
                           according to above    can determine what it is
                           if ZF = 0.            using the AH & AL settings.
                                                 However, the character is not
                                                 cleared out of the keyboard
                                                 input buffer.  i.e. do a
                                                 Int 16h w/AH=0 to clear it
                                                 out.

       2                   AL = shift status.    Get current shift status.
                          bit 0 = 1 if right shift is depressed.
                              1 = 1 if left shift is depressed.
                              2 = 1 if Ctrl is depressed.
                              3 = 1 if Alt is depressed.
                              4 = 1 if Scroll Lock is active
                              5 = 1 if Num Lock is active
                              6 = 1 if Caps Lock is active
                              7 = 1 if Insert state is active

    There are more AH subfunctions for the PC JR but who cares about the
Peanut anyway?

    I hope this helps you.

Tom Hjellming
Colorado Networks Division
Hewlett-Packard
Fort Collins, CO

...!hplabs!hpfcla!thj

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