7 2 4 8253 START MOV OUT MOV
- Slides: 60
7. 2. 4 8253的应用 START: MOV OUT MOV OUT MOV OUT • www. xju. edu. cn DX,0 FF 07 H AL,10 H DX,AL AL,56 H DX,AL AL,0 B 4 H DX,AL DX,0 FF 04 H AL,200 DX,AL DX,0 FF 05 H AL,20 DX,AL DX,0 FF 06 H AX,2000 DX,AL AL,AH DX,AL ;计数器 0的 作方式字 ;计数器 1的 作方式字 ;计数器 2的 作方式字 ;计数器 0的计数初值 ;计数器 1的计数初值 ;计数器 2的计数初值
7. 2. 4 8253的应用 +5 V 8253 A 1 GATE 0 D 0~D 7 GATE 1 GATE 2 WR CLK 0 RD CLK 1 CLK 2 A 1 A 0 译码器 CS DB IOW IOR ? • www. xju. edu. cn OUT 0 OUT 1 OUT 2
7. 2. 4 8253的应用 CNT 0: MOV DX,0123 H MOV AL,34 H OUT DX,AL MOV DX,0120 H MOV AX,20000 OUT DX,AL • www. xju. edu. cn MOV AL,AH OUT DX,AL CNT 1: …… CNT 2: ……
7. 3. 2 8255的 作方式 IOW OBF INTR ACK 输出 • www. xju. edu. cn
7. 3. 2 8255的 作方式 STB IBF INTR 来自外设的数据 IOR • www. xju. edu. cn
7. 3. 3 方式控制字及状态字 • 按位操作控制字 D 7 D 6 置位/复位 D 5 D 4 D 3 D 2 D 1 无关 位选择 • www. xju. edu. cn 000 PC 0 001 PC 1 010 PC 2 011 PC 3 100 PC 4 101 PC 5 110 PC 6 111 PC 7 D 0 0=复位 1=置位
7. 3. 3 方式控制字及状态字 A、B口 作在方式 1输出时的状态字: A组控制 D 7 D 6 D 5 D 4 B组控制 D 3 D 2 D 1 D 0 *OBF INTE INTR *OBF I/O INTE INTR I/O A 作在方式 2时的状态字: A组控制 D 7 D 6 D 5 D 4 B组控制 D 3 D 2 D 1 D 0 OBF INTE IBF INTE • www. xju. edu. cn INTR
7. 3. 4 8255的应用 8255与系统总线的连接方法 8088系统BUS D 8255 D 7 RESET D 0 ~ ~ 0 IOW IOR IOW A A 4 3 A 2 • www. xju. edu. cn RD A 1 A 0 PC 0 7 PA PC 7 0 74 LS 138 CS & G 2 A Y ≥ 1 G & C B A 2 B 0 PB ~ IOR A 1 A 0 A 15 A 14 A 13 A 12 A 11 A 10 A 9 A 8 A 7 A 5 A 6 PA ~ 7 RESET WR ~ D 7 PB 0
7. 3. 4 8255的应用 *初始化程序 INIT: MOV DX,0 FBC 3 H MOV AL,10000001 B OUT DX,AL MOV AL,00001101 B OUT DX,AL *打印一批字符的程序 MOV CX,COUNT MOV SI,OFFSET DATA GOON:MOV DX,0 FBC 2 H IN AL,DX AND AL,02 H JNZ GOON MOV AL,[SI] • www. xju. edu. cn MOV DX,0 FBC 0 H OUT DX,AL MOV DX,0 FBC 2 H MOV AL,0 OUT DX,AL MOV AL,40 H OUT DX,AL INC SI LOOP GOON HLT
7. 3. 4 • 8255的应用 题目分析: • 使 8255的A端口和B端口均 作于方式 0 • 8253计数器 0和计数器 1均 作于方式 3,利用OUT 0的输出作为计数器 1的 时钟信号,使OUT 0输出频率为 2 k. Hz • 8253两个计数器的计数初值分别为: CNT 0: 2 MHz/2 k. Hz =1000 CNT 1: 100 ms/0. 5 ms=200 * 8255的初始化 MOV DX,387 H MOV AL,82 H OUT DX,AL XOR AL,AL MOV DX,384 H OUT DX,AL • www. xju. edu. cn *8255初始化命令字: MOV DX,38 BH MOV AL,36 H OUT DX,AL MOV AL,56 H OUT DX,AL
7. 3. 4 8255的应用 *8255置计数初值: MOV DX,388 H MOV AX,2000 OUT DX,AL MOV AL,AH OUT DX,AL MOV DX,389 H MOV AL,200 OUT DX,AL • www. xju. edu. cn *8255 的控制程序 MOV DX,385 H WAITT:IN AL,DX AND AL,0 FFH JNZ WAITT MOV DX,384 H MOV AL,0 FFH OUT DX,AL ……
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