Pulldown resistor options

[SamMarrocco]

I'm using sixteen momentary switches on a pendant to control some KFlop functions using the 3.3v IO Pins on the JP connectors and connecting them to 3.3v when closed. Since some have pulldowns (150 ohms) and some do not, I was trying to be consistent with all the switches and add pulldowns to those that do not already have them. In general, no more than one switch would be closed as a time, but I can't rule out the possibility of a few being hit at once.

Is it 'recommended' that I use 150 ohm resistors as pulldowns on the IO pins that do *not* have pulldowns, and not bother with pulldowns on the IO pins that *do* already pulldowns?

[TomKerekes]

Hi Sam,

Yes that should work. 150 Ohms is needed for high speed signal termination, but for push button switches 1K should be sufficient and use less current.

[SamMarrocco]

Thank you Tom.
Just because I'm curious, is there a physical reason why the last two of the ten IO pins don't have pulldowns on JP 4 and JP6?

[TomKerekes]

Hi Sam,

Not specifically. In some cases it not helpful to have pull downs. For example "open collector" type of drive isn't possible with pull downs. Outputs can source more current without pull downs.