sleep() and waking per internal timer?

starfire151 · Joined: 01 Apr 2007 Posts: 195

I'm trying to put a PIC18LF2525 to sleep for about two minutes. I'd like to use one of internal timers to do this. Is this possible? Is there a link to a forum subject that discusses this?

I've tried a search on "sleep()" but have only found articles related to an external interrupt being input on the EXT0 pin. Unfortunately, I don't have that available as an input (it is being used as another interrupt source for a different input).

I've looked through the compiler manual and it's not clear. It looks like I could set a timer and put the chip to sleep but its not clear if the timer would continue to run or not. I looked at the chip document and it appears to be possible but there are several modes where the timer remains active and several where it is not active.

Any help would be appreciated. Crying or Very sad

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

For two minutes you probably have to use the Watchdog Timer.
Timer1 could run from an external 32.768 KHz crystal. It would roll
over every 2 seconds. Using the divide-by-8 prescaler, this could
become 16 seconds. But only the Watchdog is going to do two minutes.

libor · Joined: 14 Dec 2004 Posts: 288 Location: Hungary

I suggest to put the PIC for several shorter naps (2-16 seconds each) with the Timer1 and count these naps waking up shortly after every nap and go to sleep again if the count has not reached the desired timing.
Doing so you get a more precise and widely adjustable sleep algorithm (beyond any time limit) with almost the same average current consumption as sleeping thru all the time.

FYI: Timer1 requires an external crystal (a 32768Hz* clock crystal is used commonly) to be running during sleep.
I don't know, there may be slower crystals, are there ?

starfire151 · Joined: 01 Apr 2007 Posts: 195

Forgive my ignorance... I haven't tried to set a PIC up for sleep or WDT modes before.

Could someone please explain what exactly I need to do to set up a watchdog timer and to have my program execute from where it left off when it wakes back up after going to sleep for about 2 minutes?

I also found a reference to going into "idle" mode (more power usage than sleep but less than full operation) by using the setup_oscillator(OSC_IDLE). I tried this statement using a PIC18F2525 (with NanoWatt technology) and the CCS version 3.249 compiler, but it didn't recognize the "OSC_IDLE". Is this something new with the version 4.x compiler?

Thanks.

Dave