Question

微机原理课后习题

试编程序将内存从40000H到4BFFFH的每个单元中均写入55H,并再逐个单元读出比较,看写入的与读出的是否一致。若全对,则将AL置7EH;只要有错,则将AL置81H。

Answer 1

        CODE  SEGMENT
              ASSUME    CS:CODE
      START:
              MOV       AX,4000H
              MOV       DS,AX
              MOV       ES,AX
              MOV       CX,0C000H
              CLD
              MOV       SI,0
              MOV       DI,0
              MOV       AL,55H
              REP       STOSB

              MOV       CX,0C000H
              MOV       AL,55H
              MOV       DI,0
              REPE      SCASB
              JCXZ      @1
              MOV       AL,81H
              JMP       @2
         @1:
              MOV       AL,7EH
         @2:
              CBW
              CALL      DSPAXS
              MOV       AH,4CH
              INT       21H
;==================================
; 输出有符号数，输出的数应放 ax中 
      DSPAXS  PROC      NEAR
              PUSH      AX
              OR        AX,AX
              JNS       @DSPAXS
              NEG       AX
              PUSH      AX
              PUSH      DX
              MOV       AH,2
              MOV       DL,'-'
              INT       21H
              POP       DX
              POP       AX
    @DSPAXS:
              CALL      DSPAX
              POP       AX
              RET
      DSPAXS  ENDP
;==================================
; 输出无符号数，输出的数应放 ax中 
       DSPAX  PROC      NEAR
              PUSH      AX
              PUSH      BX
              PUSH      CX
              PUSH      DX
              PUSHF
              XOR       CX,CX
              MOV       BX,10
    @DSPAX1:
              XOR       DX,DX
              DIV       BX
              INC       CX
              OR        DX,30H
              PUSH      DX
              CMP       AX,0
              JNE       @DSPAX1
              MOV       AH,2
    @DSPAX2:
              POP       DX
              INT       21H
              LOOP      @DSPAX2
              POPF
              POP       DX
              POP       CX
              POP       BX
              POP       AX
              RET
       DSPAX  ENDP
;===========================                     
        CODE  ENDS
              END       START