Timer and counter of 51 single chip microcomputer

One · The principle of timer and counter

      They are automatically added with the input pulse of the counter 1, Every pulse , Counter auto Jia 1, When the counters are all 1 when , Then input a pulse counter back 0, And the overflow of the counter makes the corresponding interrupt flag position 1, towards CPU Make an interrupt request .          In the timing mode, it means that the time has come , In counting mode, the count is full .

Two ·    Timer structure

        timing / The counter is essentially a plus 1 Counter . It adds itself with the input pulse of the counter 1, That is, every pulse , The counter automatically adds 1,, When added to the counter, it is all 1 when , One more pulse will set the counter back to zero , And the overflow of the counter makes the corresponding interrupt flag position 1, towards CPU Make an interrupt request （ timing / When the Counter interrupt is allowed ）. If timing / The counter operates in timing mode , It means that the timing time has expired ; If working in counting mode , Indicates that the count value is full .
  so , The initial value of the count is subtracted from the value of the counter at the time of overflow 1 The count value of the counter .

3、 ... and · Timer counter structure                                                                                                                                      
      TMOD Decide whether the working mode is counting or timing ,TCON Then control the start and interrupt application of the counter timer                     working principle （ With TH0,TL0） For example ： Pulse at TL0（ low 8 position ） Add up in , After filling up ,TH0 Add 1,TL0 return 0; wait until TH1 Also accumulated after full , overflow TF0 Set up 1.                                                                                          1·TMOD          

 （1）GATE Gate control position                                                                                                                                   There are two ways to start the timer ;                                                                                                              The first one is ：GATE=0,TR0/1=1;                                                                                                            The second kind ;GATE=1,TR0/1=1;INT0/1=1;                                                                                           （2）C/T;C/T=0 For timing mode ,C/T=1 In counting mode ;                                                                         （3）M1M0

2.TCON                                                                                                                                                The upper four bits control the start and interrupt application of the timing counter , Low four bit control external interrupt

（1）TF1：T1 Overflow request flag bit .T1 When count overflows , The hardware is set automatically TF1 by 1,CPU After responding to the interrupt, the hardware automatically clears it 0.T1 Working hours ,CPU Check at any time TF1 Working state of , Once detected TF1 Set up 1,CPU Respond immediately .                  （2）TR1：T Operation control bit .TR1 Set up 1 Start working , Set up 0 Stop when .TR1 Set by software 1 or 0.                          TF0 and TR0 Be similar to TR1 and TF1.

Four · How the timer works  

1. Operation mode 0                                                                                                                                                TL0 The lower five bits of overflow forward TH0 High octave carry of ,TH0 Overflow time  , Set up TF0,TF0 towards CPU Apply for interruption   2. Operation mode 1                                                                                                                                                 16 Bit working mode ,TH0 It's the top eight ,TL0 It's eight lower                                                                           3. Operation mode 2

                                                                                                  

        For automatic reload timer