5.2.3 Crystal
The PIC18F56Q71 Curiosity Nano Board has a 32.768 kHz crystal footprint made for standard 3.2 mm by 1.5 mm surface mount crystals with two terminals.
The crystal footprint is not connected to the PIC18F56Q71 by default, as the
GPIOs are routed out to the edge connector. Some hardware modifications are required to use the crystal.
- 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, marked RA6 and RA7
- 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, J207 and J208
The crystal has a cut-strap next (J216) to it, which can be used to measure the oscillator safety factor. This 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.
Figure 5-4 shows the cut straps and solder points.
| PIC18F56Q71 Pin | Function | Shared Functionality |
|---|---|---|
| RA7 | OSC1 (Crystal input) | Edge connector |
| RA6 | OSC2 (Crystal output) | Edge connector |
