;FIFILENAME:PWM.ASM
;內容：PWM脈寬調制（小直流電機轉速控制實驗）
PORT1       EQU       290H
PORT2       EQU       28BH
PORT3       EQU       28AH
DATA        SEGMENT
BUF1        DW         ?
BUF2        DW         ?
DATA        ENDS
CODE        SEGMENT
            ASSUME  CS:CODE
START:      MOV   DX, PORT2
            MOV   AL, 8BH
            OUT   DX, AL              ;8255K口輸入
LLL:        MOV   AL, 80H
            MOV   DX, AL
            PUSH  DX
            MOV   AH, 06H
            MOV   DL, 0FFH
            INT   21H
            POP   DX
            JE    INTK               ;有無鍵按下
            MOV   AH, 4CH
            INT   21H                ;返回 DOS
INTK:       MOV   DX, PORT3
            IN    AL, DX
            TEST  AL, 01H            ;讀開關狀態
            JNZ   K0
            TEST  AL, 02H
            JNZ   K1
            TEST  AL, 04H
            JNZ   K2
            TEST  AL, 08H
            JNZ   K3
            TEST  AL, 10H
            JNZ   K4
            TEST  AL, 20H
            JNZ   K5
            JMP   LLL
K0:         MOV   BUF1,0400H  
            MOV   BUF2,0330H         ;置延時常數
DELAY:      MOV   CX, BUF1
DELAY1:     
            LOOP  DELAY1
            MOV   AL, 0FFH
            OUT   DX, AL             ;D/A 輸出5V
            MOV   CX, BUF2
DELAY2:
            LOOP  DELAY2
            JMP   LLL
K1:         MOV   BUF1,0400H
            MOV   BUF2,0400H
            JMP   DELAY
K2:         MOV   BUF1,0400H
            MOV   BUF2,0400H
            JMP   DELAY
K3:         MOV   BUF1,0400H
            MOV   BUF2,0400H
            JMP   DELAY
K4:         MOV   BUF1,0400H
            MOV   BUF2,0400H
            JMP   DELAY
K5:         MOV   BUF1,0400H
            MOV   BUF2,0400H
            JMP   DELAY
CODE        ENDS
            END   START