.MODEL SMALL
INT0     EQU       220H
INT1     EQU       221H
INT10    EQU       228H
INT11    EQU       229H
C8255    EQU       21BH
PA8255   EQU       218H
PB8255   EQU       219H
PC8255   EQU       21AH
C8253    EQU       203H
T08253   EQU       200H
T18253   EQU       201H
T28253   EQU       202H

.STACK 200H

.DATA
 TIMES DW 000FH,02FFH,04FFH,08FFH,0FFFH


.CODE
START:
    MOV AX,@DATA
    MOV DS,AX
S8255:
         MOV DX,C8255                           
         MOV AL,90H
         OUT DX,AL
         MOV DX,PB8255
         MOV AL,01H  
 
         OUT DX,AL
S8259:
         CLI          ;關中斷 
         PUSH DS   ;以下設置中斷向量
         MOV AX,0000H ;SET IRQ0
         MOV DS,AX
         MOV AX,OFFSET IRQ0
         ADD AX,0000H
         MOV SI,20H
         MOV [SI],AX
         ;MOV AX,8100H
         MOV AX,CS
         MOV SI,22H
         MOV [SI],AX
         POP DS
         ;以下設置8259工作方式
         MOV AL,13H  ;ICW1
         MOV DX,INT0
         OUT DX,AL
         MOV AL,8    ;ICW2
         MOV DX,INT1
         OUT DX,AL
         mov cx,0fffh
	 loop $
         MOV AL,9    ;ICW4
         MOV DX,INT1
         OUT DX,AL
         mov cx,0fffh
	 loop $
         MOV DX,INT1
         MOV AL,0FEH ;OCW1
         OUT DX,AL
         mov cx,0fffh
	 loop $
         MOV DX,INT0
         MOV AL,20H  ;OCW2
         OUT DX,AL
         mov cx,0fffh
	 loop $
;以下設置8253的工作方式
;使用T1，工作于方式1
S8253: 
         MOV DX,C8253
         MOV AL,71H
         OUT DX,AL
         MOV DX,T18253
         MOV BX,0
         MOV AX,TIMES[BX]
 ;賦定時初值
         OUT DX,AL
         MOV AL,AH
         OUT DX,AL
         STI       ;開中斷
         MOV CL,0  
;CL用于作PB0輸出高還是低電平的標志
;CL=0，PB0輸出低，CL=1，PB0輸出高
WAITT1:  JMP WAITT1;等待T1中斷

IRQ0:    ;中斷程序
         TEST CL,0  
;首先判斷CL狀態，根據其狀態決定輸出是高還是低
         JNZ SETPB0
CLRPB0:  ;CL=0，PB0輸出低
         MOV DX,PB8255
         MOV AL,0
         OUT DX,AL
         INC CL
         JMP LOWTIME
SETPB0:  ;CL=1，PB0輸出高
         MOV DX,PB8255
         MOV AL,01H
         OUT DX,AL
         DEC CL
;以下是通過讀入A口的數據來決定定時值
;從而達到直流電機的調速目的
;只有5中數據有效：00，01，02，04，08
         MOV DX,PA8255
         IN AL,DX
         AND AL,0FH
CMP00:
         CMP AL,00H
         JNZ CMP01
         MOV BX,0
         JMP NEXT
CMP01:
         CMP AL,01H
         JNZ CMP02
         MOV BX,0001H
         JMP NEXT
CMP02:
         CMP AL,02H
         JNZ CMP04
         MOV BX,0002H
         JMP NEXT
CMP04:
         CMP AL,04H
         JNZ CMP08
         MOV BX,0003H
         JMP NEXT
CMP08:
         CMP AL,08H
         JNZ OTHERS
         MOV BX,0004H
         JMP NEXT
OTHERS:  MOV BX,0
         JMP NEXT
LOWTIME: MOV BX,0
 ;低電平持續時間的定時值
NEXT:    ;把所要求的定時值賦給T1
         ;MOV DX,C8253
         ;MOV AL,71H
         ;OUT DX,AL
         MOV AX,TIMES[BX]
         MOV DX,T18253
         OUT DX,AL
         MOV AL,AH
         OUT DX,AL
EOI:     ;發EOI命令
         MOV DX,INT0
         MOV AL,20H
         OUT DX,AL
         STI  ;啟動中斷
         IRET ;中斷返回
    
MOV AX,4C00H ;返回操作系統
    INT 21H
END START    ;程序結束