Dears I have a collection of wires connected to xmega256, 8 for porta, 8 for port b where portb used to trig 8 ultrasonic sonsors and porta used to echo that sensors, I have implemented the measurment using two tc0 timer in input capture mode and pulse width mode and every thing is good, but with out any ultrasonic connected to the board and when I trig some pin an echo signal rises at the same sensor pin and this signal fire the timer interrupt The pins connected directly to the xmega with out pull down resistors and I have check the wiring pin by pin, i dont know the source of that echo, it just appears using the oscillator when I trig the same sensor pin and it is some times randomly appears . How can avoid that signal to prevent the timer interrupt Any same problem have faced you Thanks
What is the minimum amplitude level of the input signal to trig the capture interrupt in xmega timer
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EMI problems need full schematic of impedance and layout. – Tony Stewart EE75 Jan 15 '20 at 21:40
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This is usually specified as the Vil and Vih voltage of the GPIO - the maximum voltage guaranteed to be read as zero and the minimum voltage guaranteed to be read as logic one.
For example http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-8067-8-and-16-bit-AVR-Microcontrollers-ATxmega64A1-ATxmega128A1_Datasheet.pdf section 34.10
Check your signals with a scope.
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Good I will check , what about digital filter of event channel ,can I use it to avoid noise – Majd Kassem Jan 15 '20 at 22:18