How do you connect USB pins of a PIC® microcontroller when not using the on-chip USB function?
The following are recommended steps to connect the USB pins of a PIC® microcontroller when not using the on-chip USB function:
VBUS Can be left unconnected / floating
VUSB Even when the USB module is not enabled, connect directly to Vdd with a bypass capacitor on it (10 uF max) to limit the inrush current into the device.
D+/D- Configure as output pins driven to either state (high or low), or configure as an input with an external resistor (about 10 K) pulling it to Vdd or Vss. If configured as an input, only the pin input leakage current will be drawn through the pins (the same current would flow if the pin was connected directly to Vdd or Vss). Both options allow the pins to be used later for either input or output without significant hardware modifications.
USBID Configure as an output pin driving to either state (high or low), or configure as an input with an external resistor (about 10 K) pulling it to Vdd or Vss.
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This information can also be read at http://microchipdeveloper.com/faq:66.

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