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Setting Timers on the PIC16F688?

 
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Tom-H-PIC



Joined: 08 Sep 2003
Posts: 105
Location: New Castle, DE

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Setting Timers on the PIC16F688?
PostPosted: Tue Mar 29, 2011 7:25 am     Reply with quote

Ok I must be missing it or this PIC will not do what I think it will.
I'm working with a PIC16F688. I read the data sheet about a 100 times and tested code about the same amount. Not seeing how to make this work
I'm trying to get one of the timers to run from the 31khz oscillator.
I'm using the internal oscillator at 8Mhz for the main oscillator.
What I trying to do is operate the PIC from the main oscillator at 8Mhz and have one of the timers give a 1ms interrupt with the other timer running from the 31khz as a RTC with a 1 sec. interrupt.
If this will work some pointers on setting the configuration registers would be outstanding.
Thanks all
Tom
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Tue Mar 29, 2011 1:27 pm     Reply with quote

Look at the block diagram in the data sheet.
Quote:
FIGURE 6-1: TIMER1 BLOCK DIAGRAM

I don't see any special internal connection possibility for the internal
31 KHz oscillator.

The proper way to do an RTC, is to connect a 32.768 KHz watch crystal
to the Timer1 oscillator pins. (with two 22pf or 33pf capacitors)
Tom-H-PIC



Joined: 08 Sep 2003
Posts: 105
Location: New Castle, DE

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I concur
PostPosted: Tue Mar 29, 2011 4:00 pm     Reply with quote

Thanks for the reply!
That is the conclusion that I came to.
I was getting hung-up on section 6.2.2 of the data sheet and the statement the "Timer 1 can use the LP oscillator"
Tom
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Wed Mar 30, 2011 2:05 am     Reply with quote

That is for it's own LP oscillator on the external pins. Register 6-1, bit3.
The internal 31KHz oscillator, would not really be accurate enough for any form of timekeeping anyway....

Best Wishes
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