pic 16f877a code problem (frequency counter)

Thread Starter

sayf alawneh

Joined Aug 4, 2014
20
this code is for frequency meter project
crystal oscillator is 12 Mhz
the external pulse is a square one with 300 Khz frequency
the code is designed to measure 524 Khz with prescalar value 1:8
but it only measure up to 63Khz only do u know the reason guys ?
her is the code
C:
// LCD module connections
sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;
sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;// End LCD module connections
char i;
unsigned short cnt;
unsigned int freq_result;
// Define Messages

char message1[ ] = "Freq          Hz";

char *freq = "00000";

void Display_Freq(unsigned int freq2write) {

  freq[0] = (freq2write/10000)%10 + 48;   // extrct hundred thousnads digit
  freq[1] = (freq2write/1000)%10 + 48;    //extract thousands digit
  freq[2] = (freq2write/100)%10 + 48;    //extract hundreds digit
  freq[3] = (freq2write/10)%10 + 48;    // Extract tens digit
  freq[4] =  freq2write%10     + 48;    // Extract ones digit
Lcd_Out(1, 6, freq);                   // Display Frequency on LCD

}
  void main()
  {
  TRISB = 0;
  PORTB = 0xFF;
  TMR1H = 0x00;                         // Initialize Timer1 register
  TMR1L = 0x00;                         // Initialize Timer1 register
  T1CON = 0B00110011;                            // Timer1 on, external input RC0 and 1:8 scalling
  TMR1IF_bit = 0;                       // clear TMR1IF

  TRISC = 0xff;                         // all input
//////////////////////#LCD INITIALIZATION#////////////////////
  Lcd_Init();                        // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);                // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);           // Cursor off
/////////////////////////////////////////////////////////////
Lcd_Out(1,1,message1);                // Write message1 in 1st row
do {

   TMR1H = 0;                               // reset high byte of timer 1 (takes effect when low byte written)
   TMR1L = 0;                               // reset low byte of timer 1 (also loads in high byte now)

  Delay_ms(1000);  // Delay 0.1 Sec

  freq_result = TMR1L;                      // get low byte of timer 1 count (and read high byte to buffer)
  freq_result += TMR1H*256;                 // add in the high byte from buffer
  freq_result*=8;
  Display_Freq(freq_result);                // show the result on LCD

} while(1);  // Infinite loop
 

ericgibbs

Joined Jan 29, 2010
11,114
hi,
I dont use C, but this line is suspect... Delay_ms(1000); // Delay 0.1 Sec

If your gate is open for 1 second, and the freq input is 524KHz, and Timer1 is only 16bit.? thats 65535
 

Thread Starter

sayf alawneh

Joined Aug 4, 2014
20
hi,
I dont use C, but this line is suspect... Delay_ms(1000); // Delay 0.1 Sec

If your gate is open for 1 second, and the freq input is 524KHz, and Timer1 is only 16bit.? thats 65535
its just a mistake its a delay of 1 second i used a prescaler of 1:8 so every 8 pulses r counted as one so i can get 65535*8 frequency thats 522k frequency but i cant read more than 63k hz thats my problem :/
 

djsfantasi

Joined Apr 11, 2010
6,959
…and intermediate variables should also be 32 bit integers to avoid conversion errors. Or cast intermediate values to the target variable type.
 
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