ULPWU & PLVD on 12F635 & 16F684

[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.

[FromTheCockpit]

Hi Bruce, thanks for replying. This is how I am doing now:

@ __CONFIG _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_ON & _BOD_OFF & _CPD_ON & _IESO_OFF & _FCMEN_ON & _WUREN_OFF

OSCCON = %01100000 ' Internal 4MHz select
OPTION_REG = 0 ' internal pull-ups on/off according to value written on port
CMCON0 = 7 ' disable comparator
VRCON = 0 ' disable internal Vref
GPIO = %00000000 ' LED off on boot
TRISIO = %011001 ' GPIO.0 / 3,4= input, rest outputs
PIR1 = 0 ' clear peripheral int flags
PCON.5 = 1 ' ultra low power wakeup enabled
Include "modedefs.bas"

Main:
GPIO.0= 1 ' set data latch on GPIO.0
TRISIO.0= 0 ' GPIO.0 = output (charging cap)
PAUSEUS 100 ' charge cap for 1
TRISIO.0= 1 ' GPIO.0 = input to discharge cap
IOCA.0= 1 ' int on change enabled for GPIO.0
IOCA.4=1 ' int on change enabled for sensor @ GPIO.4
while gpio.4 : wend
INTCON= %00001000 ' global ints disabled, int on change enabled
@ SLEEP ' put PIC to sleep
GOSUB Test ' go test for under voltage condition AND send data if pin is made high by sensor
GOTO Main

Though the code is working fine for now, I would still like an opinion if the above way of doing this is the reliable way in long term.
Thanks again

[Bruce]

What exactly is it you're trying to do?

[FromTheCockpit]

I am trying to build an PIR sensor with PIC attached. My aim is to make PIC sleep and wake up like every few seconds or minutes (Which I know will be based on Res/Cap value on GPIO.0) and check for voltage OR wake up if the sensor makes its pin go high.

[Bruce]

I see. If it's battery powered, then you don't want to waste current with internal pull-ups,
and you don't want one on GPIO.0 connected to the internal ULPWU current sink.

You want GPIO.0 to charge the cap through the series resistor, go to input, and let the cap
discharge through the internal current sink. Kind of defeats the purpose if you have the pin
held high via the internal pull-up.

And, if your sensor outputs logic 1 when active, you should probably avoid the while GPIO.4
since it's detecting something when GPIO.4 = 1.

A better approach might be to read the port immediately on wake-up, find out which pin
caused the interrupt on change wake up, then jump to a routine to handle it.

Maybe something like this?

@ __CONFIG _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_ON & _BOD_OFF & _CPD_ON & _IESO_OFF & _FCMEN_ON & _WUREN_OFF

Include "modedefs.bas"

OSCCON = %01100000 ' Internal 4MHz select
OPTION_REG.7 = 1 ' turn off current hog internal pull-ups
CMCON0 = 7 ' disable comparator
VRCON = 0 ' disable internal Vref
GPIO = %00000000 ' LED off on boot
TRISIO = %011000 ' GPIO.0 / 3,4= input, rest outputs
PIR1 = 0 ' clear peripheral int flags
IOCA.0= 1 ' int on change enabled for GPIO.0
IOCA.4=1 ' int on change enabled for sensor @ GPIO.4

Main:
  IF GPIO.4 THEN HandlePIR ' goto PIR detect routine
  GPIO.0= 1 ' set data latch on GPIO.0
  TRISIO.0= 0 ' GPIO.0 = output (charging cap)
  PAUSEUS 100 ' charge cap for 1
  PCON.5 = 1 ' ultra low power wakeup enabled
  TRISIO.0= 1 ' GPIO.0 = input to discharge cap
  INTCON= %00001000 ' globals disabled, int on change enabled, clear wake up int flag bit
  @ SLEEP ' put PIC to sleep
  IF GPIO.4 THEN
    PCON.5 = 0 ' disable current sink on ultra low power wakeup
    GOTO HandlePIR ' if PIR sensor woke us up, handle it
  ELSE
    GOSUB Test ' go test for under voltage condition AND send data if pin is made high by 
  ENDIF
  GOTO Main

[FromTheCockpit]

Thanks Bruce. I am going to take your advice as it exactly was my aim towards increasing battery life. Thanks again