Hi,
Regarding the GPIOs, as it was already mention, the capacitor it is used for Bypass or Charge Pump, resister is used for limit current. We can said that a typical value it is a 1Kohm Resistor with a 0.1uF capacitor . For USB here is more detail needed,
Cables for full-speed USB must include an integrated shield. A properly designed cable offers significant EMI suppression on the conductors inside the shield. The challenge for USB compliance is preventing the high frequency energy from the PCB from being coupled to the shield. A ferrite bead may be used between the USB connector shield and PCB ground to improve the EMI from the PCB from being coupled to the cable shield.
Noise from VBUS and ground may be improved by using ferrite beads.
In the next figure, there are two 33 Ω resistors (R1 and R2) that are required for proper USB operation. The USB specification requires that the USB device have a 45 Ω single-ended or 90 Ω differential impedance. This impedance includes the impedance of the USB transceiver. The impedance of the USB transceiver is lower than the requirement of the USB specification, so the 33 Ω resistors are required to bring the device impedance within the required specification limits. At this time, all NXP microcontrollers with a fullspeed USB peripheral use 33 Ω resistors, but please check the device data sheet or reference schematics as this value may change. These resistors should be placed as close to the microcontroller as possible.
Although it is possible to use ferrite beads on the USB_DP and USB_DM signal lines in a full-speed application, it is not recommended. Capacitors C1 and C2 may be used for edge rate control and to bypass high frequency energy to ground. These capacitors should be limited to a maximum of 50 pF and should be located as close to the microcontroller as possible. The capacitors are not required for the LPC microcontrollers to meet the “eye diagram” signal testing requirements, but improvements in noise-related problems have been reported when using the capacitors. ESD protection diodes with a maximum capacitance of 50 pF are recommended on the USB_DP and USB_DM signal lines; this capacitance should be taken into consideration if the edge rate capacitors C1 and C2 are included in the schematics.
Best Regards,
Sol
