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PIC16f88 external clock for timer1

 
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ancient_one



Joined: 05 Jan 2012
Posts: 7

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PIC16f88 external clock for timer1
PostPosted: Thu Jan 12, 2012 5:46 am     Reply with quote
Hi to all,
i'm using PIC16f88 with external 20M oscillator.
So i've set up:
Code:
#FUSES HS


Now i need to use timer1 to get an interrupt every 25ms:
Code:
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_8);
set_timer1(3036);
enable_interrupts(INT_TIMER1);
enable_interrupts(global);
....
#INT_TIMER1
void TIMER1_ISR()
{
 ...
}


But interrupt handler is NEVER executed, why?
temtronic



Joined: 01 Jul 2010
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Location: Greensville,Ontario

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PostPosted: Thu Jan 12, 2012 6:31 am     Reply with quote
...
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_8);


You've got the timer setup with an EXTERNAL clock source but I'll bet you do not have a crystal and caps on the ext osc pins.

The 20MHz xtal you show is the primary( or main) clock for the PIC.

If you look read the datasheet you'll hvae some options. One, would be to add the xtal/caps to the ext osc pins another would be to use the T1_INTERNAL option to use the main clock( 20 MHz).

this is my guess.
ancient_one



Joined: 05 Jan 2012
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PostPosted: Thu Jan 12, 2012 8:20 am     Reply with quote
Sure i've got a 20M oscillator with two 22pF capacitor in OSC1-OSC2 pins
asmboy



Joined: 20 Nov 2007
Posts: 2128
Location: albany ny

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PostPosted: Thu Jan 12, 2012 5:03 pm     Reply with quote
Did you probe the drive side of TMR1 osc
to see waveform on SCOPE and counter ???
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