ULPWU & PLVD on 12F635 & 16F684

[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.

[dsicon]

ok i think i have it all now
my program isn't working right but i will figure it out now that i understand things a bit better

[FromTheCockpit]

Hi, I may be too late to ask this as this thread is few years old, but I will take my chances.
I am trying to understand internal pull up on/off along with making sure pins are low before going to sleep.
If I wish the pins to be low when the program starts is it ok to use the statement: OPTION_REG=0 : GPIO=0
Since I am trying to understand internal pull up on/off so I will ask if there is any significance of OPTION_REG=128 over what I wrote above.

Secondly,
In the following code

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}

Suppose my port (Lets say sensor attached to GPIO.1) is held low and I want PIC to wake up once it goes high, does what its suppose to do, and when it again goes low PIC goes to sleep.
At what position in the code should I check to make sure port is LOW before PIC goes to sleep.

As lets say I put "WHILE gpio.1:wend" before capacitor is charged in the main loop, I fear that port could go high again while capacitor is getting charged and pic will go to sleep with the port being high.

If I put it after the capacitor charge statement, I fear the capacitor getting discharged while waiting for the port to go low which may take 1-2 seconds.

Hope I can have some help over the two issues. Thanks a lot

[Bruce]

If I wish the pins to be low when the program starts is it ok to use the statement: OPTION_REG=0 : GPIO=0

Yes, but you might want to clear TRIS registers for any pin you want to be an output, and properly setup the
WDA and WPUDA registers first.

Since I am trying to understand internal pull up on/off so I will ask if there is any significance of
OPTION_REG=128 over what I wrote above.

Yes. Bit 7 in OPTION_REG enables or disables internal pull-ups/pull-downs. 1=disabled 0=enabled.

The 12F635 has pull-ups or pull-downs. You write to WDA to select pull-ups or pull-downs, and WPUDA to
enable or disable each one indidually.

Secondly,
In the following code

Code:
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}

Suppose my port (Lets say sensor attached to GPIO.1) is held low and I want PIC to wake up once it goes high,
does what its suppose to do, and when it again goes low PIC goes to sleep. At what position in the code should
I check to make sure port is LOW before PIC goes to sleep.

Wait for the pin to go low, clear the interrupt flag bit, then SLEEP.

As lets say I put "WHILE gpio.1:wend" before capacitor is charged in the main loop, I fear that port could go
high again while capacitor is getting charged and pic will go to sleep with the port being high.

If I put it after the capacitor charge statement, I fear the capacitor getting discharged while waiting for the
port to go low which may take 1-2 seconds.

If all you need is to wake-up on pin change with low power sleep, I wouldn't use internal pull-ups or pull-downs
or the pin-change timed wake-up with ULPWU. If your sensor holds the pin low during idle periods, I would just
let the sensor hold GPIO.1 low with interrupt-on-change enabled only for GPIO.1.