long countdown timer, how to save power?

[Kamikaze47]

Thanks Darrel. Nice work as usual.

I assume that GIE and TMR1IE have to be set in order for this to work?

The only thing i might add is TMR1H.7=1 so that it will wake up every second instead of every 2 seconds.

*edit* Was just looking at the data sheet, and half answered my own question. So now i'm assuming that I need GIE clear and TMR1IE set.

[Darrel Taylor]

I assume that GIE and TMR1IE have to be set in order for this to work.

The only thing i might add is TMR1H.7=1 so that it will wake up every second instead of every 2 seconds.

You need to leave GIE OFF, since there's no Handler for it to jump to.
But I think you're right, you may have to turn TMR1IE on to get it to Wake-Up.

TMR1H.7=1 will work too. But it's waking up twice as often as needed, and will use twice the power.

And after a month, a 1 second difference is less than the error rate, so attempting to get 1 second accuracy is futile at best.

DT

[Kamikaze47]

True enough. The only reason i may want to do it is so that i can watch the seconds count down when the LCD is switched on (will have a pushbutton in series with the LCD power so its only on when u press the button). I guess its a weigh-up between battery life and pretty counting seconds

[skimask]

True enough. The only reason i may want to do it is so that i can watch the seconds count down when the LCD is switched on (will have a pushbutton in series with the LCD power so its only on when u press the button). I guess its a weigh-up between battery life and pretty counting seconds

Should be easy enough to change the counting rate/wake up rate dynamically if you end up using the TMR1 method as described above.

[Kamikaze47]

good idea... if i tie the lcd's power pin to an input pin i can tell if the button is pressed and switch to counting seconds.

Thanks guys, u've been a big help.

[Kamikaze47]

OK, the 32.768kHz crystals I ordered finally arrived, so i'm trying to get this working, but it looks like the timer is not waking up the PIC.

I tested the timer by itself and its happily overflowing every 2 seconds, but either its not running when in sleep mode, or it is and the overflow isnt waking up the PIC.

ADCON0=%00000000
ADCON1=%01111111
T1CON=%00001111

TMR1IE VAR PIE1.0
TMR1IF VAR PIR1.0

TMR1IE=1


'... main code here - calls countdown suburoutine ...'


countdown: 
LCDOUT $FE,1,$FE,2,"Starting"
TMR1IF=0
@ SLEEP
@ NOP      
LCDOUT $FE,1,$FE,2,"Time Remaining"
GOSUB update_lcd
GOSUB update_time_vars
IF timeup=1 then RETURN
GOTO countdown

I get "Starting" displayed on the LCD, but that's it, I never see "Time Remaining".

Any ideas?

edit: config, in case its relevant:

        __CONFIG    _CONFIG1H, _INTIO2_OSC_1H 
        __CONFIG    _CONFIG2H, _WDT_OFF_2H
        __CONFIG    _CONFIG3H, _MCLRE_ON_3H
        __CONFIG    _CONFIG4L, _DEBUG_OFF_4L & _LVP_OFF_4L

[Kamikaze47]

Ok, I answered my own question

After looking at the interrupt logic diagram in the data sheet, I realised that I also had to set PEIE in order for TMR1 overflow to wake the PIC. So I added:

PEIE VAR INTCON.6
PEIE=1

And all is working good.