Oscillator and timer interference

GiG · Joined: 03 Sep 2021 Posts: 39

Hello friends, since I just started CCS, I have a series of problems with it.
I just wrote a program in which I used Timer0 and Timer1.
And I called the commands related to the timer and got the numbers according to the formula calculations of the timer.
But because I also need to use an oscillator, when I add this command to the code:

temtronic · Posted: Wed Nov 03, 2021 5:36 am

You need to tell us which PIC you're using and the compiler version !
Also your original program clock configuration.

GiG · Joined: 03 Sep 2021 Posts: 39

#include <16f1939.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP,PLL_SW,NOMCLR,NOBROWNOUT,PUT
#device ADC=10
#use delay(internal=8000000)
#INCLUDE <math.h>

this is config

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

It's clear that you want the PIC to run at 8 MHz. But then you're turning
on the PLL which makes it run 4x faster, at 32 MHz. If you don't want
that, then don't turn on the PLL.

GiG · Joined: 03 Sep 2021 Posts: 39

Ttelmah · Joined: 11 Mar 2010 Posts: 19504

The point is what you do in your code, overrides what you do in the setup.
The code line:

setup_oscillator (OSC_8MHZ | OSC_PLL_on);

says to run the oscillator at 8MHz, _and enable the PLL to give 32MHz_.

You are overriding the OSC_8MHz setup by then enabling the PLL.
The 8MHz clock does not use the PLL.....

GiG · Joined: 03 Sep 2021 Posts: 39

Ttelmah · Joined: 11 Mar 2010 Posts: 19504

I mean if you want to run at 8MHz, then the line is simply:

setup_oscillator (OSC_8MHZ);

To run at 8MHz, you don't enable the PLL.

GiG · Joined: 03 Sep 2021 Posts: 39

gaugeguy · Joined: 05 Apr 2011 Posts: 303

If you use #use delay(internal=8000000) then there is no reason to use the setup_oscillator command unless you are trying to change it to something different.

Ttelmah · Joined: 11 Mar 2010 Posts: 19504

'setup_oscillator' is the command.

The values passed to it are the 'parameters', saying what you want to set
it 'to'.
Now, the PLL can be fed from either the 8MHz oscillator, or any external
frequency using the LP, XT, HS RX or EC oscillators.
So there are two parts to the setting. The first saying 'what clock source',
and the second saying whether to enable the PLL or not.
If you enable the PLL with a legitimate clock source, then the output
frequency fed to the CPU is 4* the clock frequency.

So your command was saying 'select the 8MHz clock, then multiply this by
four'.

gaugeguy · Joined: 05 Apr 2011 Posts: 303

This is also clear if you look at the data sheet. The PLL can only accept a 4MHz - 8MHz input and generate a 16MHz - 32MHz output. When used with the internal oscillator, only the 8MHz can be connected to the PLL, producing a 32MHz clock for the processor.