[微机实验/TD-PITE] 8251 串行接口实验

Published: at 16:11

ToC

实验内容

通过 E 命令修改内存 3000H 的内容，发送到串口，然后自接受保存到 4000H 起始的内存单元中。

最后通过系统命令查看相应存储空间的数据，验证传输结果。

实验接线

通过 8254 控制波特率，将 TXD 和 RXD 相连以自收发。

代码

1
DATA8251 EQU 0600H
2
CON8251 EQU 0602H
3


4
C028254 EQU 06C4H
5
CON8254 EQU 06C6H
6


7
SSTACK SEGMENT STACK
8
  DW 64 DUP(?)
9
SSTACK ENDS
10


11
CODE SEGMENT
12
ASSUME CS:CODE
13


14
START PROC
15
  ;; INIT 8254
16
  MOV DX, CON8254
17
  MOV AL, 10110110B ;; MODE 3, SQUARE
18
  OUT DX, AL
19


20
  ;; CLK2 CONNECTED TO 1.8432MHz
21
  ;; OUT2 CONNECTED TO 8251-TRCLK
22
  ;; 1.8432E6/0X000C/16 = 9600BPS
23
  MOV DX, C028254
24
  MOV AL, 0CH
25
  OUT DX, AL
26
  MOV AL, 00H
27
  OUT DX, AL
28


29
  ;; INIT 8251
30
  CALL INIT
31
  MOV DX, CON8251
32
  MOV AL, 01111110B ;; ASYNC METHOD CONTROL WORD
33
                    ;; 01: ONE BYTE ESD/S1
34
                    ;; 11: EVEN JUDGE
35
                    ;; 11: 8 BYTES
36
                    ;; 10: 16
37
  OUT DX, AL
38
  CALL DELAY
39
  MOV AL, 00110100B ;; ASYNC COMMAND WORD
40
                    ;; 0: DISALLOW SEARCH
41
                    ;; 0: NO RESET
42
                    ;; 1: REQUEST SEND
43
                    ;; 1: RESET ERROR FLAG
44
                    ;; 0: NORMAL WORK
45
                    ;; 1: ALLOW RECEIVE
46
                    ;; 0: DATA CONSOLE NOT PREPARED
47
                    ;; 0: DISALLOW SEND
48
  OUT DX, AL
49
  CALL DELAY
50


51
  MOV DI, 4000H
52
  MOV SI, 3000H
53
  MOV CX, 10
54


55
LO:
56
  MOV AL, 00110111B ;; ASYNC COMMAND WORD
57
                    ;; DIFFERENCE: ALLOW SEND
58
  MOV DX, CON8251
59
  OUT DX, AL        ;; PREPARE 8251
60
  MOV DX, DATA8251
61
  MOV AL, [SI]
62
  OUT DX, AL        ;; SEND [SI] BYTE
63


64
  MOV DX, CON8251
65
LO_SEND:
66
  IN AL, DX ;; WAIT FOR SEND BUFFER TO BE EMPTY
67
  AND AL, 1
68
  JZ LO_SEND
69


70
LO_RECV:
71
  IN AL, DX ;; WAIT FOR RECV BUFFER TO HAVE DATA
72
  AND AL, 02H
73
  JZ LO_RECV
74


75
  MOV DX, DATA8251
76
  IN AL, DX     ;; RECEIVE FROM 8251
77
  MOV [DI], AL  ;; SAVE TO [DI]
78
  INC DI
79
  INC SI
80
  LOOP LO
81


82
FIN:
83
  JMP FIN
84


85
  MOV AX, 4C00H
86
  INT 21H
87
START ENDP
88


89
INIT PROC
90
  PUSH AX
91
  PUSH DX
92
  MOV AL, 00H
93
  MOV DX, CON8251
94
  OUT DX, AL
95
  CALL DELAY
96
  OUT DX, AL
97
  CALL DELAY
98
  OUT DX, AL
99
  CALL DELAY
100
  MOV AL, 40H
101
  OUT DX, AL
102
  CALL DELAY
103
  POP DX
104
  POP AX
105
  RET
106
INIT ENDP
107


108
DELAY PROC
109
  PUSH CX
110
  MOV CX, 0FFFFH
111
  LOOP $
112
  POP CX
113
  RET
114
DELAY ENDP
115


116
CODE ENDS
117
END START

实验过程

设置内存

4000H

3000H

选做实验

说明

将 a-z 的 ASCII 码写入 3000H，然后通过 9600 的波特率传输到 4000H。

当出现错误时停止传输，并将状态字显示在数据灯 D7-D0 上。

接线

接线有点混沌，反正能用就行（

由于数据线低位不够用了，所以我把 8255 接到了数据线高位（D8-D15），对应的 OUT 也就需要输出 AX 而非 AL 了。

总之就是下面这个样子：

代码

1
DATA8251 EQU 0600H
2
CON8251 EQU 0602H
3


4
C028254 EQU 06C4H
5
CON8254 EQU 06C6H
6


7
B8255 EQU 0642H
8
CON8255 EQU 0646H
9


10
SSTACK SEGMENT STACK
11
  DW 64 DUP(?)
12
SSTACK ENDS
13


14
CODE SEGMENT
15
ASSUME CS:CODE
16


17
START PROC
18
  ;; INIT 8254
19
  MOV DX, CON8254
20
  MOV AL, 10110110B
21
  OUT DX, AL
22


23
  MOV DX, C028254
24
  MOV AL, 0CH
25
  OUT DX, AL
26
  MOV AL, 00H
27
  OUT DX, AL
28


29
  ;; INIT 8251
30
  CALL INIT
31
  MOV DX, CON8251
32
  MOV AL, 01111110B
33
  OUT DX, AL
34
  CALL DELAY
35
  MOV AL, 00110100B
36
  OUT DX, AL
37
  CALL DELAY
38


39
  ;; INIT 8255
40
  MOV AL, 10010000B
41
  MOV DX, CON8255
42
  OUT DX, AL
43


44
  ;; INIT [3000]
45
  MOV SI, 3000H
46
  MOV AL, 61H   ;; a
47
  MOV CX, 26
48
INIT_CHAR:
49
  MOV [SI], AL  ;; SAVE TO [SI]
50
  INC AL
51
  INC SI
52
  LOOP INIT_CHAR
53


54
  MOV SI, 3000H
55
  MOV DI, 4000H
56
  MOV CX, 26
57


58
LO:
59
  MOV AL, 00110111B ;; ASYNC COMMAND WORD
60
                    ;; DIFFERENCE: ALLOW SEND
61
  MOV DX, CON8251
62
  OUT DX, AL        ;; PREPARE 8251
63
  MOV DX, DATA8251
64
  MOV AL, [SI]
65
  OUT DX, AL        ;; SEND [SI] BYTE
66


67
  MOV DX, CON8251
68
LO_SEND:
69
  IN AL, DX ;; WAIT FOR SEND BUFFER TO BE EMPTY
70
  AND AL, 1
71
  JZ LO_SEND
72


73
LO_RECV:
74
  IN AL, DX ;; WAIT FOR RECV BUFFER TO HAVE DATA
75
  TEST AL, 02H
76
  JZ LO_RECV
77


78
  TEST AL, 00111000B
79
  JNZ ERR_FIN
80


81
  MOV DX, DATA8251
82
  IN AL, DX     ;; RECEIVE FROM 8251
83
  MOV [DI], AL  ;; SAVE TO [DI]
84
  INC DI
85
  INC SI
86
  LOOP LO
87


88
FIN:
89
  JMP FIN
90


91
ERR_FIN:
92
  ;; OUTPUT TO 8255
93
  MOV DX, B8255
94
  MOV AH, AL
95
  OUT DX, AX
96


97
  MOV AX, 4C00H
98
  INT 21H
99
START ENDP
100


101
INIT PROC
102
  PUSH AX
103
  PUSH DX
104
  MOV AL, 00H
105
  MOV DX, CON8251
106
  OUT DX, AL
107
  CALL DELAY
108
  OUT DX, AL
109
  CALL DELAY
110
  OUT DX, AL
111
  CALL DELAY
112
  MOV AL, 40H
113
  OUT DX, AL
114
  CALL DELAY
115
  POP DX
116
  POP AX
117
  RET
118
INIT ENDP
119


120
DELAY PROC
121
  PUSH CX
122
  MOV CX, 0FFFFH
123
  LOOP $
124
  POP CX
125
  RET
126
DELAY ENDP
127


128
CODE ENDS
129
END START

结果

3000H

4000H

演示：数据灯

由于传输过程中没有出现问题，因此没法检测 8255 的部分是否正确。因此这里强行测试了一下（

修改上述代码的 79 行，把 JNZ 修改为 JZ。这样就能输出正确情况下的状态字了。实际的 LED 输出如下图所示：

通过 LED 我们可以读出当前的状态字：10000111。