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Input I/O port debounce time

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wealth210

New Member
Hi,
Normally,our project toy whose Ic input I/O port have 5-50ms debounce time.Those IC have put down capacitor 0.1uF and resistor 1Mohm!
My question is: whether I can cancel capacitor 0.1uF and resistor 1Mohm in order to save money. If I cancel them that mean those Input I/O port is floating,what will influence toy electronic function? Do it happen abnormal.
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi,
Normally,our project toy whose Ic input I/O port have 5-50ms debounce time.Those IC have put down capacitor 0.1uF and resistor 1Mohm!
My question is: whether I can cancel capacitor 0.1uF and resistor 1Mohm in order to save money. If I cancel them that mean those Input I/O port is floating,what will influence toy electronic function? Do it happen abnormal.

hi,
If you dont have some pullup or down and the input pin is floating its voltage level will be unpredictable and will not work correctly.

Whih PIC are you using.?
 

wealth210

New Member
Dear Eric,
Using GPC768A1,its input Port IOD0~IOD7 are without pull down resistor.
But have debounce time 32ms,how to make sure if the electronic function ok or not without pull down resistor? Thank you.
Additionaly,The reset circuit use diode+Resistor,pls see the attachment,why use diode? if I cancel diode,reset function is ok,no other wrong happen?
 

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  • Reset circuit.JPG
    Reset circuit.JPG
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BrownOut

Banned
The diode is there to discharge the capacitor when the power is turned off. Best to just leave it in.
 
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wealth210

New Member
Hi,
Thank you BrownOut.
Besides,Form the datasheet,We read that this IC GPC11768A1 is active low to reset whole system,but now It is connected 100K resistor to VDD, when Power on,Its resest pin is connected to VDD=3.6v,not low voltage or GND.How to understand this case?
 

BrownOut

Banned
In normal operation, you want the reset pin connected to VDD. But at turn on, the voltage on the capacitor is 0V ( partially because of the diode ) It takes awhile for the cap to charge up to the operating voltage VDD. During that charging time, the voltage is below the reset voltage threshold, assuming that the values of the capacitor and resistor are chosen properly. If you have a power glitch, the diode will discharge the capacitor, and the curcuit will be in reset with power returns.
 
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wealth210

New Member
Dear BrownOut,
Thank you again.
1. If this circuit cancel 0.1uf capactitor,VDD connect 100K resistor to pin Reset,
when power turn on,Wheter it can reset the whole system?
2. For RC charge circuit ,if we want pin reset get VDD voltage,it need time
t=(3~5)RC=30ms~50ms,Right?
3. How to get to know if the value of the resistor 100K and capacitor
0.1uf are chosen properly?
Thank you in advance.
 

BrownOut

Banned
1. Don't know what you're asking
2. Look at the product datasheet for reset time spec
3. Use the RC time constant and the specfication from #2 to analyze.
 
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