;********************;
;* 8255薄膜按键实验 *;
;********************;
 a8255        equ 288H    ;8255 A口    
 c8255        equ 28aH    ;8255 C口
 k8255        equ 28bH    ;8255控制口
data segment
 table1    dw 0770h,0B70h,0D70h,0E70h,07B0h,0BB0h,0DB0h,0EB0h
           dw 07D0h,0BD0h,0DD0h,0ED0h,07E0h,0BE0h,0DE0h,0EE0h    ;键盘扫描码表
 LED       DB 3FH,06H,5BH,4FH,66H,6DH,7DH,07H,7FH,6FH,77H,7CH
           DB 39h,5EH,79h,71h,0ffh                               ;LED段码表 0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f
char  db '0123456789ABCDEF'                                      ;字符表
mes   db 0ah,0dh,'PLAY ANY KEY IN THE SMALL KEYBOARD! ',0ah,0dh
       db 'IT WILL BE ON THE SCREEN! END WITH E ',0ah,0dh,'$'
 key_in db 0h
data ends

stacks segment stack    ;堆栈空间
     db 100 dup (?)
stacks ends

code segment
        assume cs:code,ds:data,ss:stacks,es:data
start:
        cli
        mov ax,data
        mov ds,ax
        mov es,ax
        mov ax,stacks
        mov ss,ax
        mov dx,offset mes       ;显示提示信息
        mov ah,09
        int 21h  
        MOV DX,k8255            ;初始化8255控制字
        mov al,81h              ;0100 0001 方式1，a,b口输出，c口高4位输出，低4位输入
        out dx,al          

main_key:
        call key                ;get a char in (key_in) and display it
        call disply               	;调显示子程序，显示得到的字符
        cmp byte ptr key_in,'E'
        jnz main_key
        mov ax,4c00h            ;if (dl)='E' return to EXIT!
        int 21h                 ;退出
        key proc near

key_loop:
        mov ah,1
        int 16h
        jnz exit                    ;pc键盘有按键则退出
       
        mov dx,c8255
        mov al,0fh
        out dx,al
        in al,dx                    ;度行扫描值
        and al,0fh
        cmp al,0fh
        jz key_loop                 ;未发现有键按下则退出
        call delay                  ;delay for amoment
        mov ah,al
        MOV DX,k8255
        mov al,88h
        out dx,al
        mov dx,c8255
        mov al,ah
        and al,0f0h
        out dx,al
        in al,dx                    ;读行扫描值
        and al,0f0h
        cmp al,0f0h
        jz key_loop                 ;未发现有按键则跳转

        mov si,offset table1        ;键盘扫描码表首地址
        mov di,offset char          ;字符表首地址
        mov cx,16                   ;带查表的大小

key_tonext:
        cmp ax,[si]                 ;cmp (col,row) with every word
        jz key_findkey              ;in the table
        dec cx
        jz key_loop                 ;未找到对应扫描码
        inc si                    
        inc si                      ;新增inc si
        inc di
        jmp key_tonext

key_findkey:
        mov dl,[di]
        mov ah,02
        int 21h                    ;显示查找到的键盘码
        mov byte ptr key_in,dl

key_waitup:
        MOV DX,k8255
        mov al,81h
        out dx,al
        mov dx,c8255
        mov al,0fh
        out dx,al
        in al,dx           ;度行扫描值
        and al,0fh
        cmp al,0fh
        jnz key_waitup     ;按键未抬起跳转
        call delay         ;delay for amoment
        ret

exit:        
        mov byte ptr key_in,'E'
        ret
key endp

delay proc near
        push ax            ;delay 50ms--100ms
        mov ah,0
        int 1ah
        mov bx,dx
delay1:
        mov ah,0
        int 1ah
        cmp bx,dx
        jz delay1
        mov bx,dx
delay2:
        mov ah,0
        int 1ah
        cmp bx,dx
        jz delay2
        pop ax
       ret
delay endp

DISPLY PROC NEAR
    	PUSH ax
    	MOV BX,OFFSET LED
    	MOV AL,byte ptr key_in
        SUB al,30h
        CMP al,09h
        JNG  DIS2
        SUB al,07h
DIS2:  
        XLAT
    	MOV DX,a8255                  ;c8255->a8255
    	OUT DX,AL                     ;输出显示数据，段码
        POP AX
    	RET
DISPLY  ENDP

code ends
end start