[微机实验/TD

实验内容

观察 8254 工作在方式 0、方式 1、方式 2 和方式 3 的波形。

实验接线

实验说明中使用的是计数器 1，但我的环境下计数器 1 之前不知道出了什么问题，无法正常使用。更换为计数器 0 则工作正常，因此以下实验均以计数器 0 实现。

现在发现好像是初值赋值的变量出问题了，但我懒得改了（

接线如下图：

将 CLK0 与时钟源的 18.432kHz 相连，GATE 与开关及 LED 现实单元的 K0 相连。

代码

C018254 EQU 0600H

C028254 EQU 0602H

C038254 EQU 0604H

CON8254 EQU 0606H

CODE SEGMENT

ASSUME CS:CODE

START PROC

MOV DX, CON8254

;; 01: COUNTER 1

;; 11: READ HIGHER 8 BYTES

;; THEN LOWER 8 BYTES

;; 000:WORK TYPE 0

;; 0: BINARY NUMBER

MOV AL, 00110000B

;;MOV AL, 00110010B

;;MOV AL, 00110100B

;;MOV AL, 00110110B

OUT DX, AL

MOV DX, C018254

MOV AL, 00H ;; LOWER 8 BYTES

OUT DX, AL

MOV AL, 48H ;; HIGHER 8 BYTES

OUT DX, AL

LO:

JMP LO

MOV AX, 4C00H

INT 21H

START ENDP

CODE ENDS

END START

C018254 EQU 0600H C028254 EQU 0602H C038254 EQU 0604H CON8254 EQU 0606H CODE SEGMENT ASSUME CS:CODE START PROC MOV DX, CON8254 ;; 01: COUNTER 1 ;; 11: READ HIGHER 8 BYTES ;; THEN LOWER 8 BYTES ;; 000:WORK TYPE 0 ;; 0: BINARY NUMBER MOV AL, 00110000B ;;MOV AL, 00110010B ;;MOV AL, 00110100B ;;MOV AL, 00110110B OUT DX, AL MOV DX, C018254 MOV AL, 00H ;; LOWER 8 BYTES OUT DX, AL MOV AL, 48H ;; HIGHER 8 BYTES OUT DX, AL LO: JMP LO MOV AX, 4C00H INT 21H START ENDP CODE ENDS END START

C018254 EQU 0600H C028254 EQU 0602H C038254 EQU 0604H CON8254 EQU 0606H CODE SEGMENT ASSUME CS:CODE START PROC MOV DX, CON8254 ;; 01: COUNTER 1 ;; 11: READ HIGHER 8 BYTES ;; THEN LOWER 8 BYTES ;; 000:WORK TYPE 0 ;; 0: BINARY NUMBER MOV AL, 00110000B ;;MOV AL, 00110010B ;;MOV AL, 00110100B ;;MOV AL, 00110110B OUT DX, AL MOV DX, C018254 MOV AL, 00H ;; LOWER 8 BYTES OUT DX, AL MOV AL, 48H ;; HIGHER 8 BYTES OUT DX, AL LO: JMP LO MOV AX, 4C00H INT 21H START ENDP CODE ENDS END START

这里值得注意的是我们将计数器初值设置成了 0x4800，这个值的十进制表示就是 18432，与时钟源的频率相同，即计数一秒。

波形

方式 0

将 GATE 输入设置为高电平，等待一秒后输出变为高电平。

方式 1

计数器在 GATE 边沿启动。书上说是上升沿，但其实下降沿也会触发。

方式 2

方式 2 我不清楚输出是否正确，仅作参考。

方式 3

方式 3 是方波输出，如下所示。

选做实验：手动控制输入时钟

连线

修改布线，将 CLK0 与 KK1+ 相连，如下图所示：

代码

C018254 EQU 0600H

C028254 EQU 0602H

C038254 EQU 0604H

CON8254 EQU 0606H

CODE SEGMENT

ASSUME CS:CODE

START PROC

MOV DX, CON8254

MOV AL, 00110000B

OUT DX, AL

MOV DX, C018254

MOV AL, 08H ;; LOWER 8 BYTES

OUT DX, AL

MOV AL, 00H ;; HIGHER 8 BYTES

OUT DX, AL

LO:

JMP LO

MOV AX, 4C00H

INT 21H

START ENDP

CODE ENDS

END START

C018254 EQU 0600H C028254 EQU 0602H C038254 EQU 0604H CON8254 EQU 0606H CODE SEGMENT ASSUME CS:CODE START PROC MOV DX, CON8254 MOV AL, 00110000B OUT DX, AL MOV DX, C018254 MOV AL, 08H ;; LOWER 8 BYTES OUT DX, AL MOV AL, 00H ;; HIGHER 8 BYTES OUT DX, AL LO: JMP LO MOV AX, 4C00H INT 21H START ENDP CODE ENDS END START

C018254 EQU 0600H
C028254 EQU 0602H
C038254 EQU 0604H
CON8254 EQU 0606H

CODE SEGMENT
ASSUME CS:CODE

START PROC
  MOV DX, CON8254
  MOV AL, 00110000B
  OUT DX, AL
  
  MOV DX, C018254
  MOV AL, 08H       ;; LOWER 8 BYTES
  OUT DX, AL
  
  MOV AL, 00H       ;; HIGHER 8 BYTES
  OUT DX, AL
  
LO:
  JMP LO

  MOV AX, 4C00H
  INT 21H
START ENDP

CODE ENDS
END START

输出

连按 KK1 即可，待计数值归零时就会变为高电平。

选做实验：周期为 1 的方波

这个实验我们在基础实验的时候就已经做完了，这里就跳过了。

选做实验：控制 LED

连线

正常连接 8255 即可。OUT0 连接 MIR6，通过中断控制 LED 移动。

代码

C018254 EQU 0600H

C028254 EQU 0602H

C038254 EQU 0604H

CON8254 EQU 0606H

CODE SEGMENT

ASSUME CS:CODE

START PROC

MOV BX, 0;

;; INIT 8255

MOV DX, 0646H

MOV AL, 90H ;; 10010000B, INPUT FROM A & OUTPUT TO B

OUT DX, AL

;; MIR6

MOV AX, OFFSET MIR6 ;; PUT CS:IP TO INTERRUPT VECTOR ADDRESS

;; 6: 38H - 3BH

;; IP -> 38H

;; CS -> 3AH

MOV SI, 38H

MOV [SI], AX

MOV AX, CS

MOV SI, 3AH

MOV [SI], AX

;; --------------------------------------------------

;; INIT 8259

CLI

MOV AL, 11H

OUT 20H, AL

MOV AL, 08H

OUT 21H, AL

MOV AL, 04H

OUT 21H, AL

MOV AL, 07H

OUT 21H, AL

MOV AL, 2FH

OUT 21H, AL

STI

;; --------------------------------------------------

MOV DX, CON8254

;;MOV AL, 00110100B

MOV AL, 00110110B

OUT DX, AL

MOV DX, C018254

MOV AL, 00H ;; LOWER 8 BYTES

OUT DX, AL

MOV AL, 48H ;; HIGHER 8 BYTES

OUT DX, AL

MOV BX, 0

LO:

JMP LO

MOV AX, 4C00H

INT 21H

START ENDP

MIR6:

CMP BL, 0FFH

JE WRITE

SHL BL, 1

INC BL

WRITE:

MOV DX, 0642H

MOV AL, BL

OUT DX, AL

IRET

CODE ENDS

END START

C018254 EQU 0600H C028254 EQU 0602H C038254 EQU 0604H CON8254 EQU 0606H CODE SEGMENT ASSUME CS:CODE START PROC MOV BX, 0; ;; INIT 8255 MOV DX, 0646H MOV AL, 90H ;; 10010000B, INPUT FROM A & OUTPUT TO B OUT DX, AL ;; MIR6 MOV AX, OFFSET MIR6 ;; PUT CS:IP TO INTERRUPT VECTOR ADDRESS ;; 6: 38H - 3BH ;; IP -> 38H ;; CS -> 3AH MOV SI, 38H MOV [SI], AX MOV AX, CS MOV SI, 3AH MOV [SI], AX ;; -------------------------------------------------- ;; INIT 8259 CLI MOV AL, 11H OUT 20H, AL MOV AL, 08H OUT 21H, AL MOV AL, 04H OUT 21H, AL MOV AL, 07H OUT 21H, AL MOV AL, 2FH OUT 21H, AL STI ;; -------------------------------------------------- MOV DX, CON8254 ;;MOV AL, 00110100B MOV AL, 00110110B OUT DX, AL MOV DX, C018254 MOV AL, 00H ;; LOWER 8 BYTES OUT DX, AL MOV AL, 48H ;; HIGHER 8 BYTES OUT DX, AL MOV BX, 0 LO: JMP LO MOV AX, 4C00H INT 21H START ENDP MIR6: CMP BL, 0FFH JE WRITE SHL BL, 1 INC BL WRITE: MOV DX, 0642H MOV AL, BL OUT DX, AL IRET CODE ENDS END START

C018254 EQU 0600H C028254 EQU 0602H C038254 EQU 0604H CON8254 EQU 0606H CODE SEGMENT ASSUME CS:CODE START PROC MOV BX, 0; ;; INIT 8255 MOV DX, 0646H MOV AL, 90H ;; 10010000B, INPUT FROM A & OUTPUT TO B OUT DX, AL ;; MIR6 MOV AX, OFFSET MIR6 ;; PUT CS:IP TO INTERRUPT VECTOR ADDRESS ;; 6: 38H - 3BH ;; IP -> 38H ;; CS -> 3AH MOV SI, 38H MOV [SI], AX MOV AX, CS MOV SI, 3AH MOV [SI], AX ;; -------------------------------------------------- ;; INIT 8259 CLI MOV AL, 11H OUT 20H, AL MOV AL, 08H OUT 21H, AL MOV AL, 04H OUT 21H, AL MOV AL, 07H OUT 21H, AL MOV AL, 2FH OUT 21H, AL STI ;; -------------------------------------------------- MOV DX, CON8254 ;;MOV AL, 00110100B MOV AL, 00110110B OUT DX, AL MOV DX, C018254 MOV AL, 00H ;; LOWER 8 BYTES OUT DX, AL MOV AL, 48H ;; HIGHER 8 BYTES OUT DX, AL MOV BX, 0 LO: JMP LO MOV AX, 4C00H INT 21H START ENDP MIR6: CMP BL, 0FFH JE WRITE SHL BL, 1 INC BL WRITE: MOV DX, 0642H MOV AL, BL OUT DX, AL IRET CODE ENDS END START

效果