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Userrr
Joined: 09 Jul 2004
Posts: 40
Location: Europe
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| Again about Frequency Measure |
 Posted: Sat Jul 10, 2004 8:50 pm |
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Anybody can tell me what is max frequency in it my example.
Don't very critic me I'm beginner ( locker ).
Or can anybory give me sample without PORTB interrupt
dir CCS\exmpl\ - Please don't
| Code: |
#include <16f876.h>
//#device ICD=TRUE
//#device adc=10
#use delay(clock=4000000)
#fuses NOWDT,XT, NOPUT, NOPROTECT, NOBROWNOUT, NOLVP, NOCPD, NOWRT//, DEBUG
#BYTE PORTA = 0x05
#BYTE PORTBN = 0x06
#BYTE PORTCN = 0x07
#BIT RB4 = PORTBN.4
#BIT RB5 = PORTBN.5
#define DelPerTimer0 122 // For 1 Second Interrupt
#include <lcd.h>
#define LCD_BLANK() {lcd_send_byte(0,1);delay_ms(2);}
int hc;
byte last_b ;
int32 freq,freq_to_lcd;
//************************************************** 1Sec / 122 Interrupt
#int_rtcc
void isr()
{
if(--hc==0)
{
freq_to_lcd=freq;
freq=0;
hc=DelPerTimer0;
}
}
//**************************************************
//************************************************** Button Press
#int_rb
rb_isr ( ) {
byte changes;
changes = last_b ^ portbn;
last_b = portbn;
if (bit_test(changes,4 )&& !bit_test(last_b,4)){
Freq++;
}
}
//***************************************************
void main() {
hc = DelPerTimer0;
set_rtcc(4);
set_tris_a(0);
set_tris_b(0xf0);
set_tris_c(0xf0);
portc=0;
setup_counters( RTCC_INTERNAL, RTCC_DIV_32);
enable_interrupts(INT_RTCC);
enable_interrupts(INT_RB);
enable_interrupts(GLOBAL);
Lcd_Init();
while (TRUE) {
last_b=PORTBN;
LCD_gotoxy( 1,1 );
printf ( LCD_PutC, "%ld Hz ", freq_to_lcd );
}
}
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[img]
http://icd2.front.ru/freqm.jpg
[/img] |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Sun Jul 11, 2004 7:10 pm |
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Thanks for providing the schematic! This makes understanding your problem much easier.
Your processor is running at 4MHz, or 1us per instruction. The handling of your port B interrupt takes:
55 instructions for the register saving and restoring.
21 instructions in the rb_isr()
You have two interrupts for every pulse, total of 152 instructions. The maximum frequency you can meassure will then be around 6500Hz.
A small note | Code: | changes = last_b ^ portbn;
last_b = portbn;
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You are here reading portB two times. There is a small theoretical chance that the value has changed in between these two reads which will cause a wrong result in your code.
Why do you make it hard on yourself by using PB4? The PB4 interrupt will occur on each edge but from your code it looks like you only want to count the frequency. Using the EXT interrupt on PB0 you will only get an interrupt on the positive or negative edge (selectable), so you get half the number of interrupts and are able to measure up to double the frequency.
Change your portB interrupt to:
| Code: | //************************************************** Button Press
#int_ext
void ext_isr ( )
{
Freq++;
}
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Total 55 + 12 = 67 instructions. Your maximum frequency goes up to 14.900Hz.
For even higher frequencies you could use the hardware CCP unit which was designed just to do this, count pulses. See the description of the setup_ccp1() function in the manual.
I'm just wondering, in your code you mention that this function is for detecting "Button Press". How are you going to handle switch bouncing? |
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Userrr
Joined: 09 Jul 2004
Posts: 40
Location: Europe
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| Thank ckielstra |
| Posted: Mon Jul 12, 2004 2:48 pm |
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Thanks for correct my errors
Please tell me max frequency :
using CCP
using RB0
using EXT_Timer |
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Userrr
Joined: 09 Jul 2004
Posts: 40
Location: Europe
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| How About |
| Posted: Tue Aug 03, 2004 11:58 am |
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How about this circuit to measure 50MHZ?
Does anyboby see for CCS?
This is for 74HC132 and PIC with RA4 - T0CKI
[img]
http://icd2.front.ru/fm.jpg
[/img] |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Tue Aug 03, 2004 12:34 pm |
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You can't measure 50Mhz with a PIC.
However, you could divide this signal down and measure it. Since you know how much the signal was divided by, you then multiply the value measured by that value. You'll lose the lower significant digits but the difference between 50.0009MHz and 50.0000MHz might not matter to you.
What exactly is your goal? |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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Userrr
Joined: 09 Jul 2004
Posts: 40
Location: Europe
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| How |
| Posted: Wed Aug 04, 2004 10:17 am |
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| How about asm code in PDF on CCS |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Wed Aug 04, 2004 11:02 am |
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| The manual explains how to embed asm code into your C file. Look for the #asm in the manual. Somehow I get the feeling that this is a school project which should be about learning and not copying someone else's work. |
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