0 V to 3.3 V, 4 mA source/sink channel

[johnnyhassle]

• Pin Description Min/Max
• AX0 to AX7 I/O channels 0 V to 3.3 V, 4 mA source/sink

I want read the voltage on pin AX0 from a AAA battery, 1.5V. My question is: what does 4 mA source/sink mean? Can I use this pin for reading de battery's voltage?

Thanks in advance

 

[HTA]

It should not be possible because it looks like an Push/Pull output driver which can source or sink 4mA. You would need an A/D converter input or an universal digital/analog I/O.

Enjoy your design work!

 

[dick_freebird]

This seems like a general purpose low voltage (not that
low, nowadays) digital port with the standard 4mA CMOS
drive strength.

It will not give you anything but a 1/0 reading from your
battery, configured as input. It will charge or discharge
your battery at a few tens of mA if you leave it as an
output (IOH, IOL specs are usually at 10%-from-rail).
This spec does not imply any analog input (A/D)
capability on the pins (although someone -could- make
a truly universal-subject-to-range-limits I/O, it seldom
has value enough to add the baggage for those who won't
use it).

A worse problem is that 1.5V sits right about logic threshold,
but you don't know on which side - only that the input
front end will be put linear with high power dissipated and
potential damage. Unless these are well designed Schmitt
inputs with current limiting to ensure they can take any
input voltage indefinitely, not the case with simple CMOS
inverter structures.

I think you need some intervening circuitry to turn volts
into bits. This could take many forms. Could be simple,
like a comparator and using another digital pin to dither
a PWM signal, low pass filter as the compare-to quantity,
and read the comparator output. Though this would use
the power rail as a primary reference, with the accuracy
issues that implies.