4.1 Crystal

The PIC18F56Q24 Curiosity Nano Board has a 32.768 kHz crystal footprint for standard 3.2 mm by 1.5 mm surface mount crystals with two terminals. The crystal footprint is not connected to the PIC18F56Q24 by default, as the GPIOs are routed to the edge connector.
Figure 4-1. 32.768 kHz Crystal Block Diagram
Table 4-1. Crystal Connections
PIC18F56Q24 PinFunctionShared Functionality
RA7OSC1Edge connector
RA6OSC2Edge connector
Some hardware modifications are required to use a crystal with the PIC18F56Q24.
  • The two I/O lines routed to the edge connector must be disconnected to reduce the chance of contention to the crystal and to remove excessive capacitance on the lines
  • Disconnect the edge connector by cutting the two cut straps on the bottom side of the board, J107 and J108. Marked RA6 and RA7 in the silkscreen
  • Connect the crystal by soldering on a solder blob on each circular solder point next to the crystal on the top side of the board, J109 and J110
  • Add suitable capacitors to C104 and C105
Figure 4-2. Crystal Cut Straps

The crystal has a cut strap (J111), which can be used to measure the oscillator safety factor and is done by cutting the strap and adding a 0402 SMD resistor across the strap. The AN2648 application note from Microchip contains more information about oscillator allowance and safety factors.