measure the xtal

[savnik]

I want to use timer0 in order to see in the LCD the frequency of crystal (internal clock). Or external on RA4
But I do not know how I begin.
I want use it , for measure xtal.

    ' 16F877A
    
   	DEFINE LCD_DREG	PORTD	      ' Selection of the port D
    DEFINE LCD_DBIT 4	          ' Selection one RD4 with RD7
    DEFINE LCD_RSREG PORTD	      ' RS on port D
    DEFINE LCD_RSBIT 2	          
    DEFINE LCD_EREG	PORTD         ' E on port D
    DEFINE LCD_EBIT 3	         
    DEFINE LCD_BITS 4		      ' Mode 4 bits
    DEFINE LCD_LINES 2	          ' 2 lines
      
    DEFINE OSC 4
       
    OPTION_REG = %00001000  
    
start:

    LCDOUT $FE,1,#TMR0
    
    goto start

[skimask]

To measure something, anything, you have to have an accurate timebase. To measure the internal clock of the PIC, using that same internal clock as your timebase as you've shown in your brief example, doesn't work.
Do you have an o'scope?

[savnik]

To measure something, anything, you have to have an accurate timebase. To measure the internal clock of the PIC, using that same internal clock as your timebase as you've shown in your brief example, doesn't work.
Do you have an o'scope?

Yes i have.
Or how to measure a xtal on RA4;
I want to measure the frequency of a oscillator with xtal or from a signal connecting to RA4

[skimask]

Yes i have.
Or how to measure a xtal on RA4;
I want to measure the frequency of a xtal or from a signal connecting to RA4

So you want to make a frequency counter then...not measure the internal frequency of your PIC...

[savnik]

So you want to make a frequency counter then...not measure the internal frequency of your PIC...

Yes.I want to measure the frequency of a oscillator with xtal or from a signal.

[skimask]

Yes.I want to measure the frequency of a oscillator with xtal or from a signal.

One of the easiest ways I can think of off the top of my head...

Use PBP's COUNT command...

But that's only good up to about 125Khz when the PIC is running at 20Mhz.

So, you could 'pre-divide' (like the various prescaler/postscalers inside the PIC) the incoming signal using a divide-by-x chip, like maybe a 74193 or something similar.

Feed the input signal into the 74193, take the output from the 74193's Qd output, which will be a divide-by-16 output, and will effectively increase PBP's COUNT commands range up to about 2Mhz (with a decrease in resolution of course).

Cascade 2 of the 74193's back-to-back, and you should be able to measure signals up to about 32Mhz (which is the effective limit of the 74LS193), using PBP's COUNT command.