微机习题课(键盘-8255A行扫描法).ppt

1,8255A并行接口(实验一),识别按键方法：行扫描法和线反转法1、行扫描法STEP1:检查是否有键按下1）所有行输出0；2）读列状态，检查是否全1；若否，则有可能有键按下3）延时20ms，再读列线，是否全1。若否，有键按下,2,STEP2:读键码（行扫描法）1）行扫描；逐行输出02）读列状态。被扫描到得行有键按下，列状态才会改变STEP3:键分析1）行值送（AL）2）列值送（AH）3）（AX）取反，得键码,3,STEP4:键处理1）查表拿键值与键值表比较，相同则记录下对应的字符码2）显示字符,4,主程序：,设置数据段，显示提示信息,调键盘扫描子程序KEY,字符是否为R,N,Y,开始,结束,5,键扫描子程序流程图（行扫描法）：,置8255A控制字82H，A口输出，B口输入,A口输出低电平，B口读入数据,标识位BL清零,列线全为高电平,(BL)=1?,Y,N,延时去抖动BL置1,N,Y,A,B,B,开始,6,第1行输出低电平,保存行值,列线全为高电平,行扫描完毕,取行值,行值左移1位指向下一行,N,Y,Y,N,A,B,C,7,与表无任一键相同,Y,在屏幕上显示此键对应的字符,从A口输出00，从B口读入列值,输入字符的ASCII码存放在(DL)中,键是否已释放,返回,Y,N,列值送(AH)，行值送(AL)，(AX)取反，查表,B,C,N,8,PA55EQU218HPB55EQU219HP55CTLEQU21BHDATASEGMENTTABLEDW0101H,0102H,0104H,0108H;键码表DW0110H,0120H,0140H,0180HDW0201H,0202H,0204H,0208HDW0210H,0220H,0240H,0280HDW0401H,0402H,0404H,0408HDW0410H,0420H,0440H,0480HCHARDBCDEF;字符码表,行扫描法源程序1of10,9,DBBA98DB4567DB3210DB;四个空格DBRPMGMESDBINPUTANYKEYINTHEDBSMALLKEYBOARD.DB0AH,0DH;回车换行DBITWILLBEDISPLAYDBONTHESCREEN!DBENDWITHR,行扫描法源程序2of10,10,DB0AH,0DH,$DATAENDSCODESEGMENTMAINPROCFARASSUMECS:CODE,DS:DATASTART:MOVAX,DATAMOVDS,AX;DS指向数据段MOVDX,OFFSETMESMOVAH,09;显示提示信息INT21HKY:CALLKEY;调键盘扫描子程序,行扫描法源程序3of10,11,CMPDL,R;键入字符不是R，转KYJNZKYMOVAX,4C00HINT21HRETMAINENDPKEYPROCNEAR;键盘扫描子程序MOVAL,82H;设置8255A控制字MOVDX,P55CTL;工作在方式0，端OUTDX,AL;口A输出，端口B输入BEGIN:MOVBL,00H;标识位清零,行扫描法源程序4of10,12,WAIT1:MOVAL,00H;端口A输出全0MOVDX,PA55OUTDX,ALMOVDX,PB55INAL,DX;端口B读入列值ANDAL,07HCMPAL,07HJZBEGIN;若为07H，无键按下CMPBL,01HJZKPRESS;若为1，已消抖动MOVCX,1000H,行扫描法源程序5of10,13,DLY:LOOPDLY;延时去抖MOVBL,01H;标识位置1JMPWAIT1KPRESS:MOVAL,0FEH;第一行输出0RSCAN:MOVDX,PA55OUTDX,ALPUSHAX;保存行值MOVDX,PB55INAL,DX;读入列值ANDAL,07HCMPAL,07H,行扫描法源程序6of10,14,JZNEXTR;列值全为1，跳转MOVAH,AL;列值送(AH)POPBX;弹出行值MOVAL,BLNOTAX;取反，得出键码MOVSI,OFFSETTABLE;键码表首址MOVDI,OFFSETCHAR;字符码表首址MOVCX,24TT:CMPAX,SI;键码相符转NNJZNNDECCX,行扫描法源程序7of10,15,JZBEGIN;比较完仍不相符跳转ADDSI,2INCDIJMPTT;继续比较NN:MOVDL,DIMOVAH,02;显示该键码对应字符INT21HPUSHDX;字符ASCII码入栈WAIT2:MOVAL,00;端口A输出全0MOVDX,PA55OUTDX,AL,行扫描法源程序8of10,16,MOVDX,PB55;从端口B读进列值INAL,DXCMPAL,0FFHJNZWAIT2;等待键释放POPDX;字符ASCII码出栈JMPDONENEXTR:POPAXCMP