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汇编源码--BRK2

51自学网 2015-09-08 http://www.51zixue.net
TITLE   BRK2 -- Break Handling Utilities ModuleTRUE            EQU     01H                     ;boolean trueFALSE           EQU     00H                     ;boolean falseBREAKINT        EQU     23H                     ;dos control-break intrptGETVECTOR       EQU     35H                     ;dos get vector functionSETVECTOR       EQU     25H                     ;dos set vector functionDOS_FUNCTION    EQU     21H                     ;dos function callBREAK           SEGMENT PUBLIC  'CODE'BREAKFLAG       DB      0H                      ;break key hit flagSAVEBRK         DD      0H                      ;saved break vec. contents                ASSUME  CS:BREAK                ASSUME  DS:NOTHING;CHECK_BREAK    checks if ctrl-break has been pressed.  It returns;true if ctrl-break has been pressed and false if it hasn't.                PUBLIC  CHECK_BREAKCHECK_BREAK     PROC    FAR                XOR     AX, AX                  ;clear ax                MOV     AL, BREAKFLAG           ;return value = breakflag                MOV     BREAKFLAG, FALSE        ;reset breakflag                RETCHECK_BREAK     ENDP;INSTALL_BREAK_HANDLER  sets up a ctrl-break interrupt handler.  It;also saves the address of the former break handler so that it can;be restored later.                PUBLIC  INST_BRK_HANDLRINST_BRK_HANDLR PROC    FAR                PUSH    DS                MOV     AL, BREAKINT            ;AL = break interrupt                MOV     AH, GETVECTOR           ;AH = dos function code                INT     DOS_FUNCTION            ;call dos                MOV     WORD PTR SAVEBRK, BX    ;save offset in int vector                MOV     WORD PTR SAVEBRK+2, ES  ;save base in int vector                MOV     AL, BREAKINT            ;AL = break interrupt                MOV     AH, SETVECTOR           ;AH = dos function code                MOV     DX, OFFSET BRK_HANDLER  ;DX = offset of brk handler                MOV     BX, CS                  ;BX = this segment                MOV     DS, BX                  ;DS = this segment                INT     DOS_FUNCTION            ;call dos                POP     DS                RETINST_BRK_HANDLR ENDP;BRK_HANDLER    is invoked by the bios when ctrl_break is pressedBRK_HANDLER     PROC    FAR                MOV     BREAKFLAG, TRUE         ;breakflag = yes, break hit                IRETBRK_HANDLER     ENDP;REMOVE_BREAK_HANDLER restores the previous ctrl-break handlerREM_BRK_HANDLR  PROC    FAR                PUSH    DS                MOV     AL, BREAKINT            ;AL = break interrupt                MOV     AH, SETVECTOR           ;AH = dos function code                MOV     DX, WORD PTR SAVEBRK    ;DX = saved 1st word                MOV     BX, WORD PTR SAVEBRK+2  ;BX = saved 2nd word                MOV     DS, BX                  ;DS = saved 2nd word                INT     DOS_FUNCTION            ;call dos                POP     DS                RETREM_BRK_HANDLR  ENDPBREAK           ENDS                END

 

 

 
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