串行接口电路.txt

实验箱中以可编程通用异步、同步收发器8251为基础

ctr53 equ 307h
chan2 equ 306h
ctr51 equ 309h
dat51 equ 308h
baud equ 1200
fact equ 16
dseg segment
way51  db 11011110b;2位停止位,奇校验,8个数据位,波特率因子16
work51 db 00110111b;异步,不做内部复位,请求发送,错误标志复位,正常工作,接收允许,数据终端准备好,发送允许
;状态d7数据装置ready,d6=0异步工作正常,d5FE,d4OE,d3PE,d2发送器空,d1接收器ready,d0发送器ready
cd53 db 10110110b
clk  dd 1193182
disp db 'connect',10,13,'$'
dseg ends
cseg segment
     assume cs:cseg,ds:dseg
start:   mov ax,dseg
       mov ds,ax
       
       mov dx,ctr53
       mov al,cd53
       out dx,al
       mov ax,word ptr clk
       mov dx,word ptr clk+2
       mov bx,baud
       div bx
       mov bx,fact
       mov dx,0
       div bx
       mov dx,chan2
       out dx,al
       mov al,ah
       out dx,al
       MOV  DX,ctr51;命令口地址
       MOV AL,00H;空操作,向命令口送任意数
       OUT DX,AL
       MOV AL,40H;内部复位(使D6=1)
       OUT DX,AL
       NOP
       MOV AL,way51;方式命令字
       OUT DX,AL
       NOP
       MOV AL,work51
       OUT DX,AL
       NOP
       
       MOV  DX,OFFSET disp
       MOV  AH,9
       INT 21H

       MOV DX,ctr51
waitcn: in al,dx
       and al,80h
       jz waitcn

       mov dx,dat51
       in al,dx
       
waitkb: mov ah,0bh
       int 21h
      and al,al
      jz rech
      mov ah,8
      int 21h
      cmp al,27
      jz pend
      mov bl,al
      mov dx,ctr51
waittec: in al,dx
      and al,1
      jz waittec
      mov dx,dat51
      mov al,bl
      out dx,al
      jmp waitkb
rech:  mov dx,ctr51
waitrec: in al,dx
       and al,2
       jz waitkb
       mov dx,dat51
       in al,dx
       mov ah,2
       mov dl,al
       int 21h
       jmp waitkb
pend:   mov ax,4c00h
       int 21h
cseg   ends
       end start