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PIC18F4620 slow clock problem

 
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Linxroot



Joined: 16 May 2011
Posts: 17

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PIC18F4620 slow clock problem
PostPosted: Wed Jan 24, 2018 6:24 am     Reply with quote

In my project the PIC18F4620, with 10MHZ crystal result in 312KHz in
while loop. Should not it be: 10MHz crystal div/4 (in the PIC internal divider)= 2.5Mhz?

CCS PCH C Compiler, Version 5.015, xxxx

I did a test code to show the problem:

Code:

#include <18F4620.h>
#device ADC=16

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOLVP                   
#FUSES NOXINST               
#FUSES NOFCMEN
#FUSES NOIESO
#FUSES HS


#use delay(crystal=10000000)


void main()
{

   while(true)
   {
      output_toggle(PIN_D5);
   }

}


The LST file:

Code:

.................... #device PIC18F4620
.................... 
.................... #list
.................... 
.................... #device ADC=16
.................... 
.................... #FUSES NOWDT                    //No Watch Dog Timer
.................... #FUSES NOBROWNOUT               //No brownout reset
.................... #FUSES NOLVP                    //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
.................... #FUSES NOXINST                  //Extended set extension and Indexed Addressing mode disabled (Legacy mode)
.................... #FUSES NOFCMEN
.................... #FUSES NOIESO
.................... #FUSES HS
.................... 
.................... 
.................... #use delay(crystal=10000000)
.................... 
.................... 
.................... void main()
00004:  CLRF   FF8
00006:  BCF    FD0.7
00008:  MOVF   FC1,W
0000A:  ANDLW  C0
0000C:  IORLW  0F
0000E:  MOVWF  FC1
00010:  MOVLW  07
00012:  MOVWF  FB4
.................... {
.................... 
....................    while(true)
....................    {
....................       output_toggle(PIN_D5);
00014:  BCF    F95.5
00016:  BTG    F8C.5
00018:  BRA    0014
....................    }
.................... 
.................... }
0001A:  SLEEP

Configuration Fuses:
   Word  1: 0200   HS NOFCMEN NOIESO
   Word  2: 1E18   PUT NOBROWNOUT BORV21 NOWDT WDT32768
   Word  3: 8700   CCP2C1 PBADEN LPT1OSC MCLR
   Word  4: 0081   STVREN NOLVP NOXINST NODEBUG
   Word  5: C00F   NOPROTECT NOCPB NOCPD
   Word  6: E00F   NOWRT NOWRTC NOWRTB NOWRTD
   Word  7: 400F   NOEBTR NOEBTRB


The result in scope:
[img]https://drive.google.com/file/d/18mpdubaDCJvmaJp9wP1ky3049EDvTaiY/view?usp=sharing[/img]

Would be an oscillator configuration problem?
temtronic



Joined: 01 Jul 2010
Posts: 5817
Location: Greensville,Ontario

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PostPosted: Wed Jan 24, 2018 6:48 am     Reply with quote

what caps are you using for the xtal?
does another xtal work
can you scope the xtal pin to confirm it's oscillating ?

does the PIC run on internal ?
Linxroot



Joined: 16 May 2011
Posts: 17

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PostPosted: Wed Jan 24, 2018 7:06 am     Reply with quote

temtronic wrote:
what caps are you using for the xtal?
does another xtal work
can you scope the xtal pin to confirm it's oscillating ?

does the PIC run on internal ?


I'm using 15 pF caps
I used 10Mhz resonator too and the result is the same
I tested the xtal pin in the scope and it run at 10Mhz (very stable)

Quote:
does the PIC run on internal ?

with these settings, it should be external clock, but really, the resulting frequency seems to be of the internal oscillator.
gaugeguy



Joined: 05 Apr 2011
Posts: 79

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PostPosted: Wed Jan 24, 2018 7:29 am     Reply with quote

10MHz crystal
/4 for internal instruction
/4 for number of instructions in loop
/2 for complete cycle (one loop high & one loop low)

10M /4 /4 /2 = 312.5k
RF_Developer



Joined: 07 Feb 2011
Posts: 820

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Re: PIC18F4620 slow clock problem
PostPosted: Wed Jan 24, 2018 7:35 am     Reply with quote

Linxroot wrote:
with 10MHZ crystal result in 312KHz in
while loop. Should not it be: 10MHz crystal div/4 (in the PIC internal divider)= 2.5Mhz?


In a word, no. While there is only one C statement in the loop, there is more than one instruction: two to do the output and one (braches are two cycle instructions I beleive) to do the loop. I'd expect the output to be 10MHz/4/4 (instructions)/2 (as the loop toggles and one cycle of the output is two loops) = 312.5KHz, which is what you report. Therefore it's working perfectly. Granted its not working as you expect, but it is working as is should.

Quote:
Would be an oscillator configuration problem?


No, actually its an unrealistic expectation problem.

PS: Cross-posted with Gaugeguy who says the same thing.
Linxroot



Joined: 16 May 2011
Posts: 17

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Re: PIC18F4620 slow clock problem
PostPosted: Wed Jan 24, 2018 9:29 am     Reply with quote

RF_Developer wrote:
Linxroot wrote:
with 10MHZ crystal result in 312KHz in
while loop. Should not it be: 10MHz crystal div/4 (in the PIC internal divider)= 2.5Mhz?


In a word, no. While there is only one C statement in the loop, there is more than one instruction: two to do the output and one (braches are two cycle instructions I beleive) to do the loop. I'd expect the output to be 10MHz/4/4 (instructions)/2 (as the loop toggles and one cycle of the output is two loops) = 312.5KHz, which is what you report. Therefore it's working perfectly. Granted its not working as you expect, but it is working as is should.

Quote:
Would be an oscillator configuration problem?


No, actually its an unrealistic expectation problem.

PS: Cross-posted with Gaugeguy who says the same thing.


Hmmm, it's true! Thank you very much for the quick response.
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