topic PCAL9714HN hardware debouncing in Other NXP Products

PCAL9714HN hardware debouncing

Thai — Mon, 18 Mar 2024 14:31:29 GMT

Hello,

I am trying to use this PCAL9714HN to sense some limit switches.

I want to implement hardware debouncing according to section 6.9; however, I don't know which oscillator I should use.

Can I just use a 16Mhz crystal oscillator like this ABM8-16.000MHZ-10-1-U-T

Thank you very much in advance.

ErikaC — Mon, 18 Mar 2024 18:22:30 GMT

Hello,

You can use 16Mhz crystal oscillator, but you should consider the Debounce counter to determinate the qualification period.

For example:

tDP = [PERIOD of EXT CLOCK] * [Debounce counter(5C)] = 62.5 ns * 10 = 625 ns (if external clock = 16 MHz, debounce count
register (5Ch) = 0Ah)

tDP = [PERIOD of EXT CLOCK] * [Debounce counter(5C)] = 62.5 ns * 255 = 15.94 μs (if external clock = 16 MHz, debounce count
register (5Ch) = FFh)

Hope this helps.

Thai — Tue, 19 Mar 2024 10:16:32 GMT

Hello,

Thank you for your response.

I have two more questions:

1. I want to sense a limit switch for a hard stop for my motor. Which oscillator frequency would you recommend?

2. I plan to use the internal pull-up for the pin, can I just connect the switch (SW1) directly to GND like this to sense when it's being pressed?

Thank you for your help.

Best,