Reading High impedance via GPIO pin

Question

Dear sir, 
 
 We have interfaced a charger ic with NRF52832. It is having a charging status pin to show completion of charge. It is having 3 states 
 1. High impedance (Battery not present or module shut down) 
 2. Low (Charging) 
 3. High (Charge complete). 
 
 I am configuring the corresponding GPIO (GPIO 29) using the function " nrf_gpio_cfg_input" and trying to read using the function "nrf_gpio_pin_read". 
 
 But my question is whether it is possible to read High impedance state.

thanks & regards, 
 Kotteeswaran.E

hmolesworth · Answer

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.

Reading High impedance via GPIO pin

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