pic 16f877a code problem (frequency counter)

Discussion in 'Embedded Systems and Microcontrollers' started by sayf alawneh, Oct 3, 2014.

  1. sayf alawneh

    Thread Starter New Member

    Aug 4, 2014
    20
    0
    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
    // 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
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    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
     
  3. sayf alawneh

    Thread Starter New Member

    Aug 4, 2014
    20
    0
    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 :/
     
  4. FroceMaster

    Member

    Jan 28, 2012
    400
    4
    Could this be the problem "unsigned int freq_result;"
    Unsigned int is from 0 to 65535, even if u multiply by 8.
     
    djsfantasi likes this.
  5. jjw

    Member

    Dec 24, 2013
    173
    31
    The variable freq_result should be 32bit long integer.
     
  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,810
    834
    …and intermediate variables should also be 32 bit integers to avoid conversion errors. Or cast intermediate values to the target variable type.
     
Loading...