Reading High impedance via GPIO pin

RE: Reading High impedance via GPIO pin

hmolesworth — Mon, 02 Sep 2019 19:56:27 GMT

Yes it is possible to infer high-impedance state. With MCP73831 a high-resistance voltage divider is required to keep the input voltage within acceptable range (as mentioned by Dmitry). With the input pin connected to the divider mid-point read the port pin twice, once with PULLDOWN enabled and once with PULLUP enabled on the port pin. If the MCP73831 is driving low, both reads will return '0'. If the MCP73831 is driving high both reads will return '1'. If the MCP73831 is High Z the first read will be '0' and the second '1'. Allow time for any distributed capacitance to charge/discharge, perhaps a few uSecs after changing the pull-down/pull-up before reading the pin..

Edit: note the resistance divider has to be low enough to prevent the 13k internal pull-up or pull-down from holding above or below the 0/1 input thresholds when the charger drives L or H; 2 x about 2k would work but that sacrifices over 1 mA through the divider.

RE: Reading High impedance via GPIO pin

Dmitry — Mon, 02 Sep 2019 19:07:43 GMT

Hi,

MCP73831 has high output level of STAT signal close to its supply voltage (charging voltage). GPIO pins of nrf52832 are limited by VDD+0.3V. Don't connect STAT pin of 73831 to GPIO directly - either use 73832 with pull-up, or add a voltage divider.

RE: Reading High impedance via GPIO pin

awneil — Mon, 02 Sep 2019 18:31:19 GMT

[quote userid="6462" url="~/f/nordic-q-a/51676/reading-high-impedance-via-gpio-pin/207488"]Presumably, this pin is intended to drive the midpoint of a pair of series-connected LEDs[/quote]

Indeed that's what the datasheet says:

RE: Reading High impedance via GPIO pin

awneil — Mon, 02 Sep 2019 18:22:54 GMT

No: In input mode, GPIO is a digital input, so it can only read 'high' or 'low' = '1' or '0'.

To read a 3rd state, you'd need to do something analogue.

The same would apply to any microcontroller - it's not specific to Nordic or nRF52.

Presumably, this pin is intended to drive the midpoint of a pair of series-connected LEDs so that either one or the other will be on - or neither in the Hi-Z state?

You should contact the chip manufacturer to see if they have any recommendations for connecting this to a microcontroller ...