Potentially dangerous to connect a button directly to an FGPA pin?

[Aclassifier]

I see that the IceCore bottons are connected directly to port pins. Should a button pin be outputted HIGH to while the button is depressed (by some coding error etc.) then I assume the iCE40HX4K won't like it? I see that since those buttons are shared with a LED, then having a serial resistor is not very feasable.

I am used to adding a serial resistor, so that the button will not take the line fully down, but - like 1/11.

I have 3 external buttons, connected over MX3. I have for a 10k external pullup as well (for less EMC, I have a 433.706 MHz radio just above the unit) and then the button would get the bottom end of a 1k to have to pull to ground. The iCE40 will then see a 1/11 of 3V3 on depressed button.

Is it advisable to add these 1k serial resistors?

[Folknology]

Is it advisable to add these 1k serial resistors?

Yes this is a good idea (The onboard choices were down to layout, lack of space etc..).

BTW if you were really worried about rf noise getting into the FPGA you could also add a small cap from button signal to ground, for a larger value it could even help debounce depending on how the buttons are used.

[Aclassifier]

Thanks! I have other boxes with buttons on my desk, and an R-R and then debouncing in SW has been causing no trouble yet. Even when the RFM69HCW (based on Semtech SX 1231) radio is set to max RF and it ticks in the desktop speakers. But I have the sender at minimum power, I just send up a floor in a wooden house.

I would debounce in Verilog (that code I could just reuse, discussed recently in Buttons refuse to behave as (I would) expect).

The 1/4λ antenna of 433 MHz is about 16.5 cm (here) and my button wires are about half of that.. 1nF/11k should short a 433 MHz so much better than nothing, across the switch. However, haven't needed that for the odd I2C and SPI lines in these boxes. Hmm.. I'll add the serial resistor only and see how it goes. That would protect the iCE40 from stupid Verilog coding and a closed button at least. I could solder caps later on.

[Aclassifier]

Is this true?

-pullup // open collector output pulls down only,
    can never source to a shorted low: low-safe
-pulldown // open emitter output pulls up only, 
    can never source to a short to plus: high-safe
// No tag: active high and low: neither short to 
    plus or ground are safe: nothing-safe