拉幕式数码管显示技术原理与分析

1．实验任务
　　用AT89S51单片机的P0.0/AD0－P0.7/AD7端口接数码管的a－h端，8位数码管的S1－S8通过74LS138译码器的Y0－Y7来控制选通每个数码管的位选端。AT89S51单片机的P1.0－P1.2控制74LS138的A，B，C端子。在8位数码管上从右向左循环显示“12345678”。能够比较平滑地看到拉幕的效果。
2．电路原理图

图4.21.1
3．系统板上硬件连线
（1）.把“单片机系统”区域中的P0.0/AD0－P0.7/AD7用8芯排线连接到“动态数码显示”区域中的a－h端口上；
（2）.把“三八译码模块”区域中的Y0－Y7用8芯排线连接到“动态数码显示”区域中的S1－S8端口上；
（3）.把“单片机系统”区域中的P1.0－P1.2端口用3根导线连接到“三八译码模块”区域中的A、B、C“端口上；
4．程序设计方法
（1）.动态数码显示技术；如何进行动态扫描，由于一次只能让一个数码管显示，因此，要显示8位的数据，必须经过让数码管一个一个轮流显示才可以，同时每个数码管显示的时间大约在1ms到4ms之间，所以为了保证正确显示，我必须每隔1ms，就得刷新一个数码管。而这刷新时间我们采用单片机的定时/计数器T0来控制，每定时1ms对数码管刷新一次，T0采用方式2。
（2）.在进行数码显示的时候，要对显示单元开辟8个显示缓冲区，每个显示缓冲区装有显示的不同数据即可。
5．程序框图
主程序框图

中断服务程序

6．汇编源程序
DISPBUF         EQU 30H
DISPCNT         EQU 38H
DISPBIT         EQU 39H
T1CNTA          EQU 3AH
T1CNTB          EQU 3BH
CNT             EQU 3CH
                ORG 00H
                LJMP START
                ORG 0BH
                LJMP INT_T0
START:          MOV DISPCNT,#8
                MOV A,#10
                MOV R1,#DISPBUF
LP:             MOV @R1,A
                INC R1
                DJNZ DISPCNT,LP
                MOV DISPBIT,#00H
                MOV T1CNTA,#00H
                MOV T1CNTB,#00H
                MOV CNT,#00H
                MOV TMOD,#01H
                MOV TH0,#(65536-1000) / 256
                MOV TL0,#(65536-1000) MOD 256
                SETB TR0
                SETB ET0
                SETB EA
                SJMP $
INT_T0:
                MOV TH0,#(65536-1000) / 256
                MOV TL0,#(65536-1000) MOD 256
                MOV A,DISPBIT
                ADD A,#DISPBUF
                MOV R0,A
                MOV A,@R0
                MOV DPTR,#TABLE
                MOVC A,@A+DPTR
                MOV P0,A
                MOV A,P1
                ANL A,#0F8H
                ADD A,DISPBIT
                MOV P1,A               
                INC DISPBIT
                MOV A,DISPBIT
                CJNE A,#08H,NEXT
                MOV DISPBIT,#00H
NEXT:           INC T1CNTA
                MOV A,T1CNTA
                CJNE A,#50,LL1
                MOV T1CNTA,#00H
                INC T1CNTB
                MOV A,T1CNTB
                CJNE A,#8,LL1
                MOV T1CNTB,#00H
                INC CNT
                MOV A,CNT
                CJNE A,#9,LLX
                MOV CNT,#00H
                MOV A,CNT
LLX:            CJNE A,#01H,NEX1
                MOV 30H,#8
LL1:            LJMP DONE
NEX1:           CJNE A,#02H,NEX2
                MOV 31H,#8
                MOV 30H,#8
                LJMP DONE
NEX2:           CJNE A,#03H,NEX3
                MOV 32H,#8
                MOV 31H,#8
                MOV 30H,#8
                LJMP DONE
NEX3:           CJNE A,#04H,NEX4
                MOV 33H,#8
                MOV 32H,#8
                MOV 31H,#8
                MOV 30H,#8
                LJMP DONE
NEX4:           CJNE A,#05H,NEX5
                MOV 34H,#8
                MOV 33H,#8
                MOV 32H,#8
                MOV 31H,#8
                MOV 30H,#8
                LJMP DONE
NEX5:           CJNE A,#06H,NEX6
                MOV 35H,#8
                MOV 34H,#8
                MOV 33H,#8
                MOV 32H,#8
                MOV 31H,#8
                MOV 30H,#8
                LJMP DONE
NEX6:           CJNE A,#07H,NEX7
                MOV 36H,#8
                MOV 35H,#8
                MOV 34H,#8
                MOV 33H,#8
                MOV 32H,#8
                MOV 31H,#8
                MOV 30H,#8
                LJMP DONE
NEX7:           CJNE A,#08H,NEX8
                MOV 37H,#8
                MOV 36H,#8
                MOV 35H,#8
                MOV 34H,#8
                MOV 33H,#8
                MOV 32H,#8
                MOV 31H,#8
                MOV 30H,#8
                LJMP DONE
NEX8:           CJNE A,#00H,DONE
                MOV 37H,#10
                MOV 36H,#10
                MOV 35H,#10
                MOV 34H,#10
                MOV 33H,#10
                MOV 32H,#10
                MOV 31H,#10
                MOV 30H,#10
LL:             LJMP DONE
DONE:           RETI
TABLE:          DB 3FH,06H,5BH,4FH,66H,6DH,7DH,07H,7FH,6FH,00H
                END
7．C语言源程序
#include
unsigned char code dispcode[]={0x3f,0x06,0x5b,0x4f,
                               0x66,0x6d,0x7d,0x07,
                               0x7f,0x6f,0x77,0x7c,
                               0x39,0x5e,0x79,0x71,0x00};
unsigned char dispbitcode[]={0xf8,0xf9,0xfa,0xfb,
                             0xfc,0xfd,0xfe,0xff};
unsigned char dispbuf[8]={16,16,16,16,16,16,16,16};
unsigned char dispbitcnt;
unsigned int t02scnt;
unsigned char t5mscnt;
unsigned char u;
unsigned char i;
void main(void)
{
  TMOD=0x02;
  TH0=0x06;
  TL0=0x06;
  TR0=1;
  ET0=1;
  EA=1;
  while(1);
}
void t0(void) interrupt 1 using 0
{
  t5mscnt++;
  if(t5mscnt==4)
    {
      t5mscnt=0;
      P0=dispcode[dispbuf[dispbitcnt]];
      P1=dispbitcode[dispbitcnt];
      dispbitcnt++;
      if(dispbitcnt==8)
        {
          dispbitcnt=0;
        }
    }
  t02scnt++;
  if(t02scnt==1600)
    {
      t02scnt=0;
      u++;
      if(u==9)
        {
          u=0;
        }
      for(i=0;i<8;i++)
        {
          dispbuf[i]=16;
        }
      for(i=0;iO:P>
        {
          dispbuf[i]=8;
        }
    }
}