4.2.4 10.00 MHz Crystal
The PIC18F57Q84 Curiosity Nano Board has a 10.00 MHz crystal mounted, the crystal used is a VXM7-9048-10M0000000 in a standard 3.2 mm by 2.5 mm package with four terminals. The 10.00 MHz crystal is accurate to within 20 ppm.
The 10.00 MHz crystal is connected to PIC18F57Q84 on RA6 and RA7, which are also routed to the edge connector through two solder points. RA6 and RA7 are disconnected from the edge connector by default to reduce the chance of an external signal causing contention with the crystal, and to remove excessive capacitance on the lines.
Next to the 10.00 MHz crystal is a cut-strap (J209), 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.
Cut straps and solder points can be seen in Figure 4-5.
| PIC18F57Q84 Pin | Function | Shared Functionality |
|---|---|---|
| RA6 | OSC2 | Edge connector |
| RA7 | OSC1 | Edge connector |
RA6 and RA7 can be used as GPIO. To do so, some hardware modifications are required.
- Disconnect the 10.00 MHz crystal by cutting the two straps on the top side of the board next to the crystal (J207, J208). The crystal should be disconnected when using the pin as GPIO, as this might harm the crystal.
- Connect the I/O lines to the edge connector by placing solder blobs on the circular solder points marked RA6 and RA7 on the bottom side of the board (J210, J211)