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;  Install a custom Interrupt 23 (Ctrl-C exception) handler

;

;  Public domain by Bob Stout

;

;  Requires MASM 5.1 or later or equivalent

;

;  Assemble with:       MASM /Mx /z ...

;                       TASM /jMASM /mx /z ...



%       .MODEL  memodel,C               ;Add model support via command

                                        ;line macros, e.g.

                                        ;MASM /Dmemodel=LARGE


        .DATA?
_origvec        dd      ?
_newvec         dd      ?

        .CODE

;

;  This is our actual ISR

;


myint23:
        call    dword PTR _newvec       ;call our handler

        iret

;

;  Call this to install  our ISR

;


ins23   PROC    USES AX BX DS ES, offs:WORD, segm:WORD
        mov     ax,3523h                ;get old vector...

        int     21h
        mov     word PTR _origvec,bx
        mov     word PTR _origvec+2,es  ;...and save it

        mov     ax,offs                 ;load handler offset...

        mov     word PTR _newvec,ax
        mov     ax,segm                 ; & segment into _newvec

        mov     word PTR _newvec+2,ax
        push    cs                      ;get myint23 segment in DS

        pop     ds
        mov     dx, OFFSET myint23      ;install myint23 in int 23h

        mov     ax,2523h
        int     21h
        ret
ins23   ENDP

;

;  Call this to uninstall our ISR

;


redo23  PROC    USES AX BX DS
        mov     dx, word PTR _origvec   ;restore original vector

        mov     ds, word PTR _origvec+2
        mov     ax,2523h
        int     21h
        ret
redo23  ENDP

        end


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