Reset Button Functionality: Pulling High vs. Pulling Low

[tenacity2986]

EASY QUESTION, URGENT RESPONse

when u typically hit a reset buton on a breadboard, it is usually closing the circuit to ground.

However let's say u want the reset button to power to vdd when hit and be grounded when not hit. How would u implement this?

 

[vk6kro]

Connect it as in the attached diagram.

The 4.7 K resistor holds the reset pin low except if you push the switch, when the reset pin will go high.

 

[MATLABdude]

Connect it as in the attached diagram.

The 4.7 K resistor holds the reset pin low except if you push the switch, when the reset pin will go high.

We usually pull low (with the resistor in vk6kro's diagram attached to the Vdd, and GND attached to the switched terminal, a.k.a. a pull-up configuration) to ensure that the pin always sees ground.

I was burnt on this once when I used the BJT side of some optoisolators with pull-downs (and, to boot, calculated values to drive the optos near the edge of saturation). Unfortunately, the high impedance supply meant that I had a voltage divider with the pull-down resistor. This worked great when I tested with the bench supply and with some experimental switch flipping. It didn't work so great when it was exposed to the 4kHz PWM.

Moral of the story: use your function generator and oscilloscope!

 

[vk6kro]

lets say u want the reset button to power to vdd when hit and be grounded when not hit. How would u implement this?

That was the question. Why pull low when the question asks for reset to be pulled high?

Some chips require a high on the reset pin to reset. You don't get a choice.

 

[MATLABdude]

lets say u want the reset button to power to vdd when hit and be grounded when not hit. How would u implement this?

That was the question. Why pull low when the question asks for reset to be pulled high?

Some chips require a high on the reset pin to reset. You don't get a choice.

True. Just thought I'd add some enrichment discussion. (If, in fact, it's deemed as such).