8086仿真的问题用8253和8255A实现流水灯，求大神解答 -

DATA SEGMENT
      COTR EQU 00F6H
      PB_A EQU 00F0H
      PC_A EQU 00EEH
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE,DS:DATA
  START: MOV DX,00EEH
      MOV AL,00110111B
               OUT DX,AL
               MOV DX,00E8H
               MOV AL,50H
               OUT DX,AL
               MOV DX,00E8H
               MOV AL,00H
               OUT DX,AL
               MOV AX,DATA
               MOV DS,AX
               MOV DX,COTR
               MOV AL,10000001B
               OUT DX,AL
               MOV DX,00EEH
               MOV AL,00110111B
               OUT DX,AL
               MOV DX,00E8H
               MOV AL,50H
               OUT DX,AL
               MOV DX,00E8H
               MOV AL,00H
               OUT DX,AL
               MOV DX,PB_A
               MOV AL,0FCH
               OUT DX,AL
         LOO: MOV DX,PB_A
               OUT DX,AL
               PUSH AX
         AGAIN:IN AL,0F4H
               MOV AH,AL
               IN AL,0F4H
               CMP AL,AH
               JZ AGAIN
               POP AX
               ROL AL,1
               JMP LOO
      CODE ENDS
      END START