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8255如何用8255和拨动开关控制控制步进电机的正转和逆转

code   segment   
            assume   cs:code,ds:code   
                  org   100h   
  start:   jmp   begin   
  table     db   05h,15h,14h,50h,51h,41h,45h       ;相序表   
    
  begin:   mov   ax,cs   
                mov   ds,ax   
                mov   dx,303h         ;8255初始化   
                mov   al,81h   
                out   dx,al   
                .........             ;打开开关   
  get1:     mov   cl,8   
  font     mov   si,offset   table   
                mov   dx,301h   
                mov   al,[si]   
                out   dx,al               ;开始转动   
                .........               ;延时   
  wait:     mov   dx,302h   
                in     al,dx   
                and   al,01             ;判断是否拨动开关   
                jz     back             
                dec   cl   
                jnz   font   
                jmp   get1   
    
  get2:     mov   cl,8   
  back:     mov     si,table+7   
                mov   al,[si]   
                out   dx,al                 
                .........               ;延时   
  wait:     mov   dx,302h   
                in     al,dx   
                and   al,01             ;判断是否拨动开关   
                jz     font             
                dec   cl   
                jnz   back   
                jmp   get2   
                    
                ........               ;关闭电机   
              mov   ah,4ch   
              int   21h   
  code     ends   
              end   start   
  ---------------------------------------------