Options for waking up a 16LF877A while in sleep() mode?

JimB · Posted: Thu Oct 12, 2006 1:32 pm

I am using the 16LF877A device in my project. I have a single pushbutton going to pin 24 (RA2). I have a square wave signal generated by the micro, fed back to pin 8 (RB0/INT). Now I want to use the processors "sleep()" feature, but from what I am able to determine, the only way to wake the processor is to use the RBO/INT or use the MCLR. I assume the latter would reset the software to start all over, which I do not want. Since the square wave starts when the pushbutton is pushed is there another way to awaken the processor?

Also I could not find a spec on the processors current draw during sleep mode. Is there a significant drop in current? The project manager doesn't want to have an ON/Off switch if possible. The entire circuit now draws 19mA when no square wave is running since I disable most of the rest of the electronics, except for the crystal oscillator which only draws a couple of mA except for when the button is pushed, the square starts and all other devices are enabled as needed. These are an RS232 chip, negative voltage generator and 6 opamps.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Mattr0 · Joined: 27 Mar 2005 Posts: 30

you could use the watchdog timer to wake up the micro every so often to check you push button. You will sacrifice you sleep current a bit though

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

If its only sleeping lightly, how about an alarm clock?
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Guest · Posted: Sat Oct 14, 2006 3:53 pm

Since I am generating the square wave with the micro's "CCP1" output and feeding it back to RB0/INT to trip the L to H edge flag, could there be a way to set this flag internally, i.e. without an external path to the external interrupt? This would leave the RBO/INT input available for triggering the "wake" function. I'm just not experienced enough to determine this.

Mattr0 · Joined: 27 Mar 2005 Posts: 30

you should look at RB4 - RB7. These pins can be configured to create an interupt on there state change this should wake up the micro.

Ttelmah · Guest

JimB · Posted: Fri Oct 20, 2006 2:57 pm

I think that there is information here that will help me, but some clarification is needed. From the previous help statements, I think that it is being assumed that the CCP1 timer runs all the time, which it doesn't.
The CCP1 output square wave that I now have fed back to RBO/INT only runs when I use the pushbutton. The button push turns on the oscillator, a bunch of external electronics and runs until enough data is taken, then it stops and waits for another push of the button. I used the RBO/INT to generate the external L to H edge interrupt flag which starts a delay time and then tells the A/D to read the data at a fixed time after the L to H edge occurs. Since the square wave signal is generated in the micro perhaps this L to H edge setting of the interrupt flag may be internally accessable without using the RBO/INT pin and I can then use it to wake up the micro. It is this intertal access to the L to H edge flag that I don't know whether it is possible to do or not. It would also be desireable to use the same pushbutton for the wake up and also run the device.