原创 16．定时计数器T0作定时应用技术（二）

1．      实验任务<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

用AT89S51的定时/计数器T0产生2秒钟的定时，每当2秒定时到来时，更换指示灯闪烁，每个指示闪烁的频率为0.2秒，也就是说，开始L1指示灯以0.2秒的速率闪烁，当2秒定时到来之后，L2开始以0.2秒的速率闪烁，如此循环下去。0.2秒的闪烁速率也由定时/计数器T0来完成。

2．      电路原理图

3、实现程序

1．      汇编源程序

TCOUNT2S                EQU 30H

TCNT02S                    EQU 31H

ID                                 EQU 32H

                                      ORG 00H

                                      LJMP START

                                      ORG 0BH

                                      LJMP INT_T0

START:                        MOV TCOUNT2S,#00H

                                     MOV TCNT02S,#00H

                                     MOV ID,#00H

                                      MOV TMOD,#01H

                                      MOV TH0,#(65536-50000) / 256

                                      MOV TL0,#(65536-50000) MOD 256

                                      SETB TR0

                                      SETB ET0

                                      SETB EA

                                      SJMP $

INT_T0:                      MOV TH0,#(65536-50000) / 256

                                      MOV TL0,#(65536-50000) MOD 256

                                      INC TCOUNT2S

                                      MOV A,TCOUNT2S

                                      CJNE A,#40,NEXT

                                      MOV TCOUNT2S,#00H

                                      INC ID

                                      MOV A,ID

                                      CJNE A,#04H,NEXT

                                      MOV ID,#00H

NEXT:                          INC TCNT02S

                                      MOV A,TCNT02S

                                      CJNE A,#4,DONE

                                      MOV TCNT02S,#00H

                                      MOV A,ID

                                      CJNE A,#00H,SID1

                                      CPL P1.0

                                      SJMP DONE

SID1:                            CJNE A,#01H,SID2

                                      CPL P1.1

                                      SJMP DONE

SID2:                           CJNE A,#02H,SID3

                                      CPL P1.2

                                      SJMP DONE

SID3:                            CJNE A,#03H,SID4

                                      CPL P1.3

SID4:                            SJMP DONE

DONE:                        RETI

                                      END

2．      C语言源程序

#include <AT89X51.H>

unsigned char tcount2s;

unsigned char tcount02s;

unsigned char ID;

void main(void)

{

  TMOD=0x01;

  TH0=(65536-50000)/256;

  TL0=(65536-50000)%256;

  TR0=1;

  ET0=1;

  EA=1;

  while(1);

}

void t0(void) interrupt 1 using 0

{

  tcount2s++;

  if(tcount2s==40)

    {

      tcount2s=0;

      <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />ID++;

      if(ID==4)

        {

          ID=0;

        }

    }

  tcount02s++;

  if(tcount02s==4)

    {

      tcount02s=0;  //在开始运行程序的前0.2s内是没有LED闪烁的，在到0.2s是，tcount0.2s置零

      switch(ID)

        {

          case 0:

            P1_0=~P1_0;

            break;

          case 1:

            P1_1=~P1_1;

            break;

          case 2:

            P1_2=~P1_2;

            break;

          case 3:

            P1_3=~P1_3;

            break;

        }

    }

}

4、总结

LED亮到不亮转换的时间间隔是0.2s，则灯亮的时间间隔是0.4s，在2s的时间间隔你可以看到LED灯亮5次