5.2.3 Crystal
The PIC18F16Q40 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 PIC18F16Q40 by default, as the
GPIOs are routed out to the edge connector. To use the crystal, some hardware modifications
are required.
- 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 RA4 and RA5.
- Connect the crystal by soldering on a solder blob on each of the circular solder points next to the crystal on the top side of the board, J210 and J211.
The crystal has a cut-strap next (J209) 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. More information about oscillator allowance and safety factor can be found in the AN2648 application note from Microchip.
The cut straps and solder points can be seen in Figure 5-4.
| PIC18F16Q40 Pin | Function | Shared Functionality |
|---|---|---|
| RA4 | SOSCO (Crystal output) | Edge connector |
| RA5 | SOSCI (Crystal input) | Edge connector |