It’s in Table 39-7 of the AVR128DB’s datasheet. As a digital input, the impedance is in the MΩ range. V_IL is max 0.2 Vdd (0.66 V @ 3V3) and V_IH is min 0.8 Vdd (2.64 V @ 3V3).
Adding to that, the internal pull-up will be used when a volt-free switch is expected. (See Data sheet - 39.4.4 I/O Pin Characteristics)
Apologies @Staedford - @Gwil reminded me these are straight to the Pi, so slightly different.
V_IH min is 2V0
V_IL max is 0V8
Input impedance is on the order of 500K.
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Thanks @awjlogan , @Robert.Wall I was not aware that the DHW input was directly into the pi, I had assumed some protection/conditioning cctry. I will refer to the datasheet.
I can beat that - Fortran 4.
That’s good, you win.
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@Robert.Wall oh no, wait