Hi,
I'm unable to understand why resistors are connected in series with switch (R36 & R37). Kindly share your thoughts. I'm attaching a reference schematic below.

















Thanks

 

otherwise mcu-gpio72 and mcu-gpio84 will be grounded when switch is on.

 

You never want I/O lines on a processor to "float" at an undefined voltage level. The 56KΩ resistor to 3.3 V is a "weak" pullup. The 2.2KΩ is a "strong" pulldown to GND. The terms "weak" and "strong" in this context are relative.

 

otherwise mcu-gpio72 and mcu-gpio84 will be grounded when switch is on.

So, if switch is grounded then what is the problem? Isn't it similar to connecting GPIO to logic-0?

 

You never want I/O lines on a processor to "float" at an undefined voltage level. The 56KΩ resistor to 3.3 V is a "weak" pullup. The 2.2KΩ is a "strong" pulldown to GND. The terms "weak" and "strong" in this context are relative.

I agree 56k is required for known state, but when switch is connected to GND why do we need a series resistor?

 

but when switch is connected to GND why do we need a series resistor?

If the GPIO pin is inadvertently set to be a high output, the high output would be shorted to ground when the switch is pressed.

I must admit, it's not a fault condition I've ever worried about. The important point is that the voltage divider formed by the two resistors when the switch is pressed allows the I/O line to be less than the maximum voltage that's considered a low level.