PORT_A EQU 0FF9H;8255A端口地址
PORT_B EQU 0FFBH;8255B端口地址
PORT_CTL EQU 0FFFH;8255C端口地址
;数据段定义,键盘扫描表
DATA	SEGMENT	
; 
TABLE DB 77H,7B,7D,7E,0B7H,0BBH,0BDH,0BEHDB 0D7H,0DBH,0DDH,0DEH,0E7H,0EBH,0EEH
DATA ENDS
;堆栈段
STACK SEGMENT	STACKDW 50 DUP(0)
TOP_STACK LABEL	WORD	
STACK ENDS
;代码段
CODE SEGMENT	ASSUME	CS:CODE,DS:DATA,SS:STACK
MAIN: MOV AX,STACKMOV DX,AX;LEA	SP	TOP_STACKMOV AX,DATAMOV DX,AX
;初始化8255A输出BC输入
MOV DX, PROT_CTL
MOV AL,10001011B
OUT DX,AL	
;向每一行清0
MOV	AL,0
MOV DX,PORR_A
OUT DX,AL
MOV DX,PORT_B
;读列看是否有键被按下
WAIT_OPEN:
IN AL,DX
AND AL,0FH
CMP	AL,0FH
JNE WAIT_OPEN
WAIT_PRES:
IN AL,DX
AND AL,0FH
CMP	AL,0FH
JE WAIT_PRES	
MOV CX 16EAH
DELAY: LOOP DELAY
IN AL,DX
AND AL,0FH
CMP AL,0FH
JNZ WAIT_PRES
;键还是被压着,确定哪一个
MOV AL,0FEH
MOV CL,AL
NEXT_ROW:MOV DX,PORT_AOUT DX,ALMOV DX,PORT_BIN AL,DXAND AL,0FHCMP AL,0FHJNE ENCODEROL	CL,01MOV AL,CLJMP NEXT_ROW	
;找到了一对低电平
ENCODE:MOV BX,000FHIN AL,DX
NEXT_TRY:CMP AL,TABLE[BX]JE DONEDEC BXJNS NEXT_TRYMOV AH,01HJMP EXITDONE:MOV AL,BLMOV AH,00EXIT: HLT	
CODE	ENDSEND