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本電子時鐘主要是由AT89S51單片機及8個共陽數(shù)碼管組成。由于數(shù)碼管引腳比較多，占用單片機的I\O口也比較多，由于單片機最多只有32個I\O口，在數(shù)碼管比較多時(兩個以上)，就滿足不了實際需要，因此在數(shù)碼管比較多時，采用動態(tài)掃描的方式使數(shù)碼管逐個點亮。本電子時鐘就是采用的這種顯示方式。利用取表指令“MOV DPTR,#TABLE與MOVC A,@A+DPTR”和條件轉(zhuǎn)移指令“CJNE A,#data,rel”所要顯示的時間送入單片機的端口（P0口和P2口）并放大后，驅(qū)動數(shù)碼管顯示出所要顯示的具體時間。采用單片機內(nèi)部定時器定時，計數(shù)，時間非常準確！ 顯示的時間格式為：12—00—00，即“小時—分鐘—秒”。P0口為數(shù)碼管的各段位接口，P2口為8個數(shù)碼管的電源端。P3.2口為“小時”調(diào)整，P3.3口為“分鐘”調(diào)整，P3.4口為“秒”調(diào)整。但每個調(diào)整鍵只能加，不能減。晶振為12MHZ。 匯編源程序如下：
SECOND EQU 30H MINITE EQU 31H HOUR EQU 32H HOURK BIT P3.2 MINITEK BIT P3.3 SECONDK BIT P3.4 DISPBUF EQU 40H DISPBIT EQU 48H T2SCNTA EQU 49H T2SCNTB EQU 4AH TEMP EQU 4BH ORG 00H LJMP START ORG 0BH LJMP INT_T0 START:MOV SECOND,#00H MOV MINITE,#00H MOV HOUR,#12 MOV DISPBIT,#00H MOV T2SCNTA,#00H MOV T2SCNTB,#00H MOV TEMP,#0FEH LCALL DISP MOV TMOD,#01H MOV TH0,#(65536-2000) / 256 MOV TL0,#(65536-2000) MOD 256 SETB TR0 SETB ET0 SETB EA WT:JB SECONDK,NK1 LCALL DELY10MS JB SECONDK,NK1 INC SECOND MOV A,SECOND CJNE A,#60,NS60 MOV SECOND,#00H NS60:LCALL DISP JNB SECONDK,$ NK1:JB MINITEK,NK2 LCALL DELY10MS JB MINITEK,NK2 INC MINITE MOV A,MINITE CJNE A,#60,NM60 MOV MINITE,#00H NM60:LCALL DISP JNB MINITEK,$ NK2:JB HOURK,NK3 LCALL DELY10MS JB HOURK,NK3 INC HOUR MOV A,HOUR CJNE A,#24,NH24 MOV HOUR,#00H NH24:LCALL DISP JNB HOURK,$ NK3:LJMP WT DELY10MS:MOV R6,#10 D1:MOV R7,#248 DJNZ R7,$ DJNZ R6,D1 RET DISP:MOV A,#DISPBUF ADD A,#8 DEC A MOV R1,A MOV A,HOUR MOV B,#10 DIV AB MOV @R1,A DEC R1 MOV A,B MOV @R1,A DEC R1 MOV A,#10 MOV @R1,A DEC R1 MOV A,MINITE MOV B,#10 DIV AB MOV @R1,A DEC R1 MOV A,B MOV @R1,A DEC R1 MOV A,#10 MOV@R1,A DEC R1 MOV A,SECOND MOV B,#10 DIV AB MOV @R1,A DEC R1 MOV A,B MOV @R1,A DEC R1 RET INT_T0:MOV TH0,#(65536-2000) / 256 MOV TL0,#(65536-2000) MOD 256 MOV A,#DISPBUF ADD A,DISPBIT MOV R0,A MOV A,@R0 MOV DPTR,#TABLE MOVC A,@A+DPTR MOV P0,A MOV A,DISPBIT MOV DPTR,#TAB MOVC A,@A+DPTR MOV P2,A INC DISPBIT MOV A,DISPBIT CJNE A,#08H,KNA MOV DISPBIT,#00H KNA:INC T2SCNTA MOV A,T2SCNTA CJNE A,#100,DONE MOV T2SCNTA,#00H INC T2SCNTB MOV A,T2SCNTB CJNE A,#05H,DONE MOV T2SCNTB,#00H INC SECOND MOV A,SECOND CJNE A,#60,NEXT MOV SECOND,#00H INC MINITE MOV A,MINITE CJNE A,#60,NEXT MOV MINITE,#00H INC HOUR MOV A,HOUR CJNE A,#24,NEXT MOV HOUR,#00H NEXT:LCALL DISP DONE:RETI TABLE:DB 0C0H,0F9H,0A4H,0B0H,99H,92H,82H,0F8H,80H,90H,0BFH TAB:DB 0FEH,0FDH,0FBH,0F7H,0EFH,0DFH,0BFH,07FH END 本程序已通過實踐驗證�。�！
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