Proffieboard V1 and V2:
From Datasheet Table 22: 6.3.1 “General Operating Conditions”
All I/O except TT_xx:
Min(Min(VDD, VDDA, VDDUSB, VLCD)+3.6V, 5.5V)
The translation being all I/O except TT_xx are 5V tolerant.
TT_xx IO are 3.3V tolerant only (with a ±0.3 tolerance for variance)
The TT_xx Pins on Proffieboard V1/V2:
(the ones that aren’t 5V tolerant)
Extracted From Datasheet Table 15
| MCU Pin | V1 Function | V2 Function |
|---|---|---|
| 13 | Free1/Data4 | vtest, internal |
| 14 | vtest, internal | Free1/Data4 |
| 15 | SD Card SCLK, internal | SD Card SCLK, internal |
So the only effective pin you can’t use as a pulldown button pin (besides the obvious) on both the V1 and V2 are the respective Data4 pins.
Proffieboard V3:
From Datasheet Table 23 6.3.1 “General Operating Conditions”
All I/O except TT_xx:
Min(Min(VDD, VDDA, VDDUSB)+3.6V, 5.5V)
Similarly this means that all non-TT_xx pins are 5V tolerant, and still TT_xx I/O are 3.3V tolerant only.
The TT_xx Pins on Proffieboard V3:
(the ones that aren’t 5V tolerant)
Extracted From Datasheet Table 16
| MCU Pin | V3 Function |
|---|---|
| G3 | SD Power Enable, internal |
| H3 | Data4 |
| F4 | Unused |
So once again, the pin you can’t use on the V3 is still Data4.
I did say I needed to look into this eventually (among other things), so I figured I may as well do the work and make it pretty for others 