用89C2051做的数字频率计

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measure.c51 ====================================

/************************************************************************/
/*         */
/*  Frequency Meter 5Hz ... 125MHz Test Program  */
/*         */
/*  Author: Peter Dannegger     */
/*   danni@specs.de     */
/*         */
/************************************************************************/
#include \"main.h\"
#include \"measure.h\"
#include \"display.h\"
#include <stdio.h>

#define BAUD 9600

void main( void )
{
  uchar idata s[DISPLAYMEM];
  PCON |= SMOD_;    // initialization UART
  SCON = TI_ + REN_ + SM1_;
  TMOD = T1_M1_ + T0_M0_ + T0_M1_;  // T0: splitt timer
      // T1: baud rate
  TH1 = (uchar) -(0.5 + XTAL / 12.0 / 16 / BAUD);
  TL1 = -1;

  for(;;){
    measure_start();
    while( measure_poll() == 0 );
    display( measure_read(), s );
    puts( s );
  }
}

============= measure.h ==================================================

void measure_start( void );

bit measure_poll( void );

float measure_read( void );

========== display.c51 =====================================================

/************************************************************************/
/*         */
/*  Display 5 digit floating point number   */
/*         */
/*  Author: Peter Dannegger     */
/*   danni@specs.de     */
/*         */
/************************************************************************/
#include \"main.h\"

void display ( float val, uchar idata *ptr )
{
  uchar hz, num, i, dp;

  for( dp = 1; val >= 10; dp++ ) // normalize (x.xxxx)
    val *= 0.1;    // 3 times faster as \"val /= 10;\"

  hz = 0;
  if( dp > 6 ){    // MHz ?
    dp -= 6;
    hz = 'M';
  }
  if( dp > 3 ){    // kHz ?
    dp -= 3;
    hz = 'k';
  }

  for( i = DIGITS;; ){   // 5 digits
    *ptr++ = (num = val) + '0';  // get digit
    if( --dp == 0 ){   // set decimal point
      *ptr++ = '.';
    }
    if( --i == 0 )
      break;
    val = (val - num) * 10;  // next digit
  }
  if( hz )
    *ptr++ = hz;