pic 16f684 clock question

[jkmadsci]

I am trying to make a 16f684 clock program. I plan on using batteries.
If i use the int rc osc 31k hz clock, will it drift according to temperature and voltage. I read the datasheet and it said the external rc clock would drift. I didnt see any info regarding internal rc drift?

I suppose if the 31k osc drifts around too much ill have to use the 125k osc.

 

[Pommie]

I'm not familiar with that particular pic but, assuming it's the same as most other pics, to do a clock type program. Run the processor at 4MHz using the internal oscillator and use a 32.768kHz (8000h) Crystal as the external clock for timer 1. You can then use the special events trigger of ccp1 to generate a 1Hz interrupt.

If you use a RC oscillator to generate interrupts then you will have a very inaccurate clock.

To setup Timer1 and CCP1, do:

		movlw	B'00001111';             enable timer1 
		movwf	T1CON;                     with external clock

		movlw	low(8000h-1);            Lets interupt every second
		movwf	CCPR1L;                    using the special event trigger on timer 1
		movlw	high(8000h-1)
		movwf	CCPR1H
		movlw	B'00001011';              enable special event trigger on CCP1
		movwf	CCP1CON;	

		bsf	STATUS,RP0
		bsf	PIE1,CCP1IE;            enable CCP1 interrupt
		bcf	STATUS,RP0

		movlw	0C0h
		movwf	INTCON;                    enable Peripheral interrupts

And your interrupt would look something like:

interrupt	movwf	int_work
		swapf	STATUS,W
		movwf	int_status;                  status is nibble swaped
		bcf	STATUS,RP0

		bcf	PIR1,CCP1IF;             reset special event trigger interupt
		incf	Seconds;                   increment seconds as a second has passed
		
		swapf	int_status,W
		movwf	STATUS
		swapf	int_work,F;                swap to file
		swapf	int_work,W;               swap to work
		retfie

HTH

Mike.

 

[Nigel Goodwin]

I am trying to make a 16f684 clock program. I plan on using batteries.
If i use the int rc osc 31k hz clock, will it drift according to temperature and voltage. I read the datasheet and it said the external rc clock would drift. I didnt see any info regarding internal rc drift?

I suppose if the 31k osc drifts around too much ill have to use the 125k osc.

The internal oscillator is ONLY RC, it's far too inaccurate to use as a clock.

If you want clock type accuracy, use an external 32KHz watch cyrstal as Pommie suggests.