实验现象:
在示波器上观察到类似方波的波形(形如101010100)
实验代码:
1 Con_8253 EQU 0B003H
2 T2_8253 EQU 0B002H
3 CTL_ADDR EQU 0F001H
4 DATA_ADDR EQU 0F000H
5 _STACK SEGMENT STACK
6 DW 100 DUP(?)
7 _STACK ENDS
8 CODE SEGMENT
9 ASSUME CS:CODE
10 START: CALL INIT_8253
11 CALL INIT_8251
12 A1: CALL SEND
13 MOV CX,0FFFH
14 A2: MOV AX,01E0H
15 A3: DEC AX
16 JNZ A3
17 LOOP A2
18 JMP A1
19 INIT_8253 PROC NEAR
20 MOV DX,Con_8253
21 MOV AL,96H
22 OUT DX,AL
23 MOV DX,T2_8253
24 MOV AL,26H
25 OUT DX,AL
26 RET
27 INIT_8253 ENDP
28 INIT_8251 PROC NEAR
29 CALL Reset_8251
30 MOV DX,CTL_ADDR
31 MOV AL,7EH
32 OUT DX,AL
33 CALL DLTIME
34 MOV AL,31H
35 OUT DX,AL
36 CALL DLTIME
37 RET
38 INIT_8251 ENDP
39 Reset_8251 PROC NEAR
40 MOV DX, CTL_ADDR
41 MOV AL,0
42 OUT DX,AL
43 CALL DLTIME
44 OUT DX,AL
45 CALL DLTIME
46 OUT DX,AL
47 CALL DLTIME
48 MOV AL,40H
49 OUT DX,AL
50 CALL DLTIME
51 RET
52 Reset_8251 ENDP
53 DLTIME PROC NEAR
54 MOV CX,10
55 LOOP $
56 RET
57 DLTIME ENDP
58 SEND: MOV AL,55H
59 MOV DX,DATA_ADDR
60 OUT DX,AL
61 RET
62 CODE ENDS
63 END START