ULPWU & PLVD on 12F635 & 16F684

[dsicon]

Hi all
anyone one have any experience using the ULPWU (ultra low power wake up) module on the PIC12F635 ?
it seems to have started life in the PIC16F684
looking for any tips or code snips using PBP

i need to also use the PLVD (programmable low voltage detect) module but at 20+ uA i don't have the power budget to leave it on all the time for low battery warning indication

so my thought is to use the ULPWU (if i can figure it out) and wake up once in a while and enable the PLVD to sniff the battery

at first read it looks like the ULPWU will interrupt and wake up the unit roughly every 30ms using a 1000pf cap
this way too often for me, guess i could keep a counter or something

but using PBP it is not clear to me how to proceed
make the pin an output, set HI briefly, turn it back to an input and go to sleep?
something like that ?

TIA
ds

[Bruce]

Well, that was interesting. I've never used ULPWU or PLVD yet, but I have used the 12F635
in a ton of applications.

Out of curiosity, I put this together to tinker with today, and it works just like the book says.

You'll probably want to experiment with the series resistor & cap value. As voltage drops, the
wake up frequency increases, so you'll need to find some happy medium there to work in your
own application. I used a 200ohm series resistor with 1kpF cap.

@ DEVICE PIC12F635,MCLR_OFF,INTRC_OSC_NOCLKOUT,WDT_OFF,BOD_OFF
@ DEVICE PWRT_ON,FCMEN_OFF,IESO_OFF,WUREN_OFF,PROTECT_OFF

    SYMBOL PROBE = GPIO.1  ' scope probe indicates wakeup from sleep
    SYMBOL PLVD_LED = GPIO.2
    
    OSCCON = %01100000 ' Internal 4MHz select
    OPTION_REG = 128   ' internal pull-ups off 
    CMCON0 = 7         ' disable comparator
    VRCON = 0          ' disable internal Vref
        
    GPIO = %00000000   ' LED off on boot
    TRISIO = %00000001 ' GPIO.0 = input, rest outputs
    PIR1 = 0           ' clear peripheral int flags
    PCON.5 = 1         ' ultra low power wakeup enabled
    
Main:
    GPIO.0 = 1         ' set data latch on GPIO.0
    TRISIO.0 = 0       ' GPIO.0 = output (charging cap)
    PAUSEUS 24         ' charge cap for 24uS
    TRISIO.0 = 1       ' GPIO.0 = input to discharge cap
    IOCA.0 = 1         ' int on change enabled for GPIO.0
    INTCON = %00001000 ' global ints disabled, int on change enabled
    @ SLEEP            ' put PIC to sleep
    TOGGLE PROBE       ' indicate ULPWU wake up from sleep & clear mismatch
    INTCON.0 = 0       ' clear wake up on change int flag
    GOSUB TestVolts    ' go test for under voltage condition
    GOTO Main          ' not sure what this does...;o}

TestVolts:
    INTCON.6 = 1       ' peripheral ints enabled
    LVDCON = %00010101 ' enable PLVD. set trip point to 4.0V
    
    ' enable PLVD interrupt only when PLVD internal Vref is stable
    IF LVDCON.5 = 1 THEN PIE1.6 = 1 ' if stable, enable
    
    IF PIR1.6 = 1 THEN ' voltage <= 4.0V?
       HIGH PLVD_LED   ' yes. indicate voltage is <= 4.0V
       PIR1.6 = 0      ' clear int flag
    ELSE
       LOW PLVD_LED    ' else, indicate voltage is > 4.0V
    ENDIF
    LVDCON = 0         ' PLVD disabled before returning to sleep
    INTCON.6 = 0       ' peripheral ints disabled
    PIE1 = %00000000   ' low voltage detect int disabled
    RETURN
    
    END

At 5 volts it wakes up around every 30mS, and trips PLVD at <= 4.0 V.

[dsicon]

wow that's great Bruce, thanks a lot
you got farther along than i did, but this was pretty much what i was thinking about
doing

i think i will go to a 0.1mf cap for about 3 seconds

question
do you see a way to distinguish this ULPWU interrupt from some other pin that may have caused wake up from SLEEP ?
i don't

also
in your example code PROBE is for your scope and not directly related to the ULPWU pin, when you
TOGGLE PROBE
your comment says 'clear mismatch register'
does this mean that writing to any pin will clear the mismatch ?
i thought there was a mismatch bit for each pin ?

[Bruce]

question
do you see a way to distinguish this ULPWU interrupt from some other pin that may have
caused wake up from SLEEP ? i don't

If you had int on change enabled for more pins, you would need to read the port & look for
a change immediately on wake up. Other interrupts would set the flag bit associated with
that interrupt. I don't see any specific flag bit for ULPWU alone.

also
in your example code PROBE is for your scope and not directly related to the ULPWU pin, when
you TOGGLE PROBE

Yes. I just used this pin for the scope to see the timing when using different cap and resistor
values.

your comment says 'clear mismatch register' does this mean that writing to any pin will clear
the mismatch ?

A normal wake up on change requires you to read or write to the port to clear the
mismatch condition. Then clear the interrupt flag bit.

i thought there was a mismatch bit for each pin

The only pin that affects wake up on change is the one that has this feature enabled, and
is an input. There aren't any mismatch bits, but there are individual interrupt on change
enable and disable bits in IOCA.

You can remove the TOGGLE PROBE & INTCON.0 = 0 after. This gets taken care of before
the sleep instruction.

[dsicon]

thanks again Bruce,

I have one main input pin which needs to wake up the unit

so what you are saying is that if it is NOT that pin when it comes out of SLEEP then by elimination it must be the ULPWU pin ?

so then i would check the state of that pin, i.e. there is no bit that says which specific pin caused the wake up ? (i know there is not for the ULPWU)

also sorry if i am being dense here but can you explain the mismatch deal some more?
so if i read or write to *any* pin it will clear that mismatch?

[Bruce]

I have one main input pin which needs to wake up the unit

so what you are saying is that if it is NOT that pin when it comes out of SLEEP then by elimination it must be the ULPWU pin?

Yes. Assuming you don't have anything else enabled that could cause the wake up from
sleep.

so then i would check the state of that pin, i.e. there is no bit that says which specific pin caused the wake up ? (i know there is not for the ULPWU)

Yes.

also sorry if i am being dense here but can you explain the mismatch deal some more?

Sure. Say you have GPIO.1 configured for wake up. It's normally held high.

When a switch or other external device pulls this pin low, you want the PIC to wake up.
Wait for GPIO.1 to go high (by reading the port pin). Normally it will be held high by an
external or internal pull-up.

Once it's in the high state, enable wake up on change, then put the PIC to sleep.

Once it goes low, there's a mismatch, and it wakes up. Wait for the pin to return high, and
go through the process again. If the PIC enters sleep mode again, before the port pin was
returned high, then it will wake up again once the pin returns high.

so if i read or write to *any* pin it will clear that mismatch?

Yep. As long as it's a pin on that port, but I normally read the whole port into a variable,
then test for the bit in question.

Testing several bits in a row leaves too much time for another one to change.