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im reading a arm based mcu board schematic and there is 100R resistor (R30) at external 25MHz oscillator source. What is the main reason of using serial resistor at clock line ?

schematic

İsmail Fatih ILTAR
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  • https://electronics.stackexchange.com/a/7737/80284, this resistor will be important if traces are long, or there's significant mismatch in impedance between the endpoints. – Anonymous Mar 26 '18 at 11:12
  • Or just for EMI reduction by reducing slope steepness. The schmitt trigger input of the CPU will still produce a clean squarewave as clock. – Jogitech Mar 26 '18 at 11:16
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    Reducing reflections caused by a low-impedance source driving a square wave into a high-impedance load. – TonyM Mar 26 '18 at 11:29
  • So how can i determine the right value for my design? 100R is typically for it ? – İsmail Fatih ILTAR Mar 26 '18 at 11:39

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