Determine if a pullup is on a PIN or if it is floating

ke4pjw

I did something like this on the P1, per @"Phil Pilgrim (PhiPi)" , to detect if a pin had a pullup on it, or if it was floating. It works incredibly reliably.

Can this also be done on the P2? I don't know if PINF is a FLTL or FLTH.

PINL(55)
PINF(55)
if PINR(55) == 1
    ' Pin has a pullup 

JonnyMac

If you're looking for an external pull-up, you may want to use pinclear() so that any internal connections are removed.

ke4pjw

So something like this?

PINL(55)
PINCLEAR(55)
if PINR(55) == 1
    ' Pin has a pullup 

I am going to give this a swing tonight. Thanks!

JonnyMac

I tend to be cautious, so I might do this:

 pub has_xpullup(pin)

  pinclear(pin)
  pinlow(pin)
  pinfloat(pin)

  return pinread(pin) == 1

evanh

An extra cautiousness would be to have a known delay between the float and the pin read. Then a faster execution won't inadvertently sample before the pull-up crosses the threshold.

 pub has_xpullup(pin)

  pinclear(pin)
  pinlow(pin)
  pinfloat(pin)
  waitus(1)

  return pinr(pin)

ke4pjw

I had to use float low. I suspect pinfloat is the same at FLTH.

Thanks guys!

PUB HardwareVer() : r
  PINCLEAR(ENC_P) 
  org
    DRVH #ENC_P
    FLTL #ENC_P
    DRVL #ENC_P
    FLTL #ENC_P
  end
  waitus(1)
  debug(udec_(PINREAD(ENC_P)))
  if PINREAD(ENC_P) == 1
          ' Pin has a pullup 
    debug("Version 2 hardware")
    r := 2
  else
    debug("Version 1 hardware")
    r := 1
  return r

evanh

Why is that DRVH there? Did it help in some way?

Ariba

Another possibility on the P2 is to enable a weak internal pulldown resistor and then read the input. Any external pullup lower then the internal pulldown will pull the input high. This doesn't depend on timing.

  wrpin(PIN, P_LOW_150K)      'enable internal pulldown of 150k
  pinl(PIN)
  if pinr(PIN)                'an external pullup will pull it high 
     'there is a pullup
  pinclear(PIN)               'disable internal pulldown

Andy

evanh

Hehe, one step further is use the compDAC pin mode to measure a floating ADC - https://forums.parallax.com/discussion/174441/measuring-floating-pin-voltage-adc-from-just-the-built-in-comparator

  wrpin(PIN, P_LOW_150K)      'enable internal pulldown of 150k
  pinl(PIN)
  if sar_reading(PIN) > 5    'an external pullup will pull it high 
     'there is a pullup
  pinclear(PIN)               'disable internal pulldown

This will work well with even very high pull-up resistances.

ke4pjw

Thanks guys, all around! What I have works but I will keep these in my back pocket. I am using a 100K pullup.

evanh

Oops, the pin mode above doesn't combine with the SAR routine. CompDAC pin mode can do a 1k5 pull-down though. So still a possible approach there,

evanh

You know, I'm gonna add this to the SD driver code. The confusion that occurs if the pull-ups aren't in place are worth the extra code to check for them. Good reminder Terry. Thanks.