Microchip Technology MA180021 Manuale Utente
PIC18F87J50 FS USB Plug-In Module User’s Guide
DS51678A-page 12
© 2007 Microchip Technology Inc.
FIGURE 3-1:
KEY COMPONENT LOCATIONS
3.3
CRYSTAL
In order to use the USB module on the PIC18F87J50 family of microcontrollers, the
module requires a fixed 48 MHz or 6 MHz clock for use in Full-Speed or Low-Speed
modes, respectively. These clock frequencies can be derived from the internal 96 MHz
PLL, and the microcontroller core need not run at the same frequency as the USB
module. In order to use the 96 MHz PLL, a clock source which is an integer multiple of
4 MHz is required. A 12 MHz crystal is included on the board for this purpose.
On the PIC18F87J50 microcontroller, the oscillator pins (RA6 and RA7) route directly
to the 12 MHz crystal. Unlike most other I/O pins, these do not route directly to the “ICE
Module” female headers. Two resistor pads can be used to connect RA6 and RA7 to
the female header pins, but by default, these are left unpopulated. This is done to
prevent “crystal contention” between the 12 MHz crystal on the PIM and the 10 MHz
crystal on the HPC Explorer board.
module requires a fixed 48 MHz or 6 MHz clock for use in Full-Speed or Low-Speed
modes, respectively. These clock frequencies can be derived from the internal 96 MHz
PLL, and the microcontroller core need not run at the same frequency as the USB
module. In order to use the 96 MHz PLL, a clock source which is an integer multiple of
4 MHz is required. A 12 MHz crystal is included on the board for this purpose.
On the PIC18F87J50 microcontroller, the oscillator pins (RA6 and RA7) route directly
to the 12 MHz crystal. Unlike most other I/O pins, these do not route directly to the “ICE
Module” female headers. Two resistor pads can be used to connect RA6 and RA7 to
the female header pins, but by default, these are left unpopulated. This is done to
prevent “crystal contention” between the 12 MHz crystal on the PIM and the 10 MHz
crystal on the HPC Explorer board.
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3
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7
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5
1
JP
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JP1
JP
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