RESET switch needs a time delay why?

[danny davis]

RESET switch needs a time delay why?

Most RESET switch in digital circuit when I press them the logic levels goes from high to low and the low state DC voltage rises up very slowly back up

Is this called Rise time? when the DC voltage ( straight linear line on the oscilloscope, NO SLOPE ) rising from zero to +5 volts?

Rise time to mean is when you have a triangle waveform, it rising at a slope

 

[pplus]

RESET switch needs a time delay why?

Most RESET switch in digital circuit when I press them the logic levels goes from high to low and the low state DC voltage rises up very slowly back up

In order to have time to complete the transition process.

Is this called Rise time?

No.Rise time refers to the change ramp pulse (square, triangle).

 

[ashugtiwari]

with MCU's with active low reset signal, this circuit is used which is as u mentioned in the question:
Here in normal condition, C1 cuts off Vcc from GND and so to MCU reset pin, active high signal is given.
when the reset button is pressed, there is discontinuous change in signal from high to low at MCU input reseting it, since MCU pin is connected directly to GND through switch.
When switch is released, C1 wont allow voltage to change from low to high quickly but it will take time to charge to Vcc voltage, that time is rise time and is determined by time constant t=R1*C1 as in ckt.

Hope that helps.

 

[danny davis]

No.Rise time refers to the change ramp pulse (square, triangle).

So what is it called if it's not called rise time? when a reset switch is active low reset

The DC voltage takes time from zero voltages DC to rise up to the supply voltage, but its a straight DC line , not sure what this is called?

 

[pplus]

So what is it called if it's not called rise time? when a reset switch is active low reset

The DC voltage takes time from zero voltages DC to rise up to the supply voltage, but its a straight DC line , not sure what this is called?

Agree. My fault.

 

[Zaphappy]

Rise time usually refers to the time is takes to go from 10% to 90% of peak voltage (assuming little overshoot). Probably not that important for your problem unless you have multiple gates that depend on accurate timing between each other.

If your looking for a specific terminology used in digital engineering I'm not sure there is one ??? More important would be the time to trigger threshold level.

 

[danny davis]

Yes it's not called rise time because its not a slope. A RC Intergrator network charges a capacitor at a slope, the capacitor in the active low reset switch charges the capacitor not at a slope but at a straight dc level why is that?

 

[danny davis]

An RC Integrator network charges a capacitor at a slope

The capacitor in the "active low reset switch" charges the capacitor, but it's not at a slope, it's DC level a straight dc level that rises up slowly. How are the capacitors difference?

One capacitor charges at a slope, the other capacitor charges at a straight line DC level rising up to supply voltage ( but what is this called, it's not rise time cause it's not a slope?

Rise time is for slopes and ramps

This is a DC level straight line that moves from zero voltage and slowly rises up to supply voltage, but what is this called please? it's not a rise time

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An RC Integrator network charges a capacitor at a slope

The capacitor in the "active low reset switch" charges the capacitor, but it's not at a slope, it's DC level a straight dc level that rises up slowly. How are the capacitors difference?

One capacitor charges at a slope, the other capacitor charges at a straight line DC level rising up to supply voltage ( but what is this called, it's not rise time cause it's not a slope?

Rise time is for slopes and ramps

This is a DC level straight line that moves from zero voltage and slowly rises up to supply voltage, but what is this called please? it's not a rise time

 

[Zaphappy]

Are you certain the other cap isn't charging with a slope ? Perhaps looking at the waveform with more horizontal resolution will show whats going on. Every sharp edged pulse I have seen have some slope to it, just might be faster than your equipment. Unless your simulating this with Spice, then look at your analysis parameters, you might be missing something...