On the AVR64DD32 Curiosity Nano board is a mounted 24.00 MHz crystal of type VXM7-9062-24M0000000. The crystal is accurate to within 20 ppm. Using the External High-Frequency Crystal Oscillator (XOSCHF) module in AVR64DD32 with the mounted 24.00 MHz crystal generates a clock signal that is significantly more accurate than the Internal High-Frequency Oscillator (OSCHF) module. With the Auto-Tune feature, the 24 MHz can be used as a reference to improve the accuracy of the internal oscillator.
The 24.00 MHz crystal is connected to AVR64DD32 on PA0 and PA1, which are also routed to the edge connector through two solder points. PA0 and PA1 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 24.00 MHz crystal is a cut-strap (J216) that can be used to measure the oscillator safety factor, which is done by cutting the strap and adding a 0402 SMD resistor across the strap. The AN2648 application note from Microchip contains detailed information about the oscillator allowance and safety factor.
Figure 1 shows cut straps and solder points..
| AVR64DD32 Pin | Function | Shared Functionality |
|---|---|---|
| PA0 | XTALHF1 (Crystal input) | Edge connector |
| PA1 | XTALHF2 (Crystal output) | Edge connector |
Some hardware modifications are required to use PA0 and PA1 as a GPIO.
- Disconnect the 24.00 MHz crystal by cutting the two straps on the top side of the board next to the crystal (J214, J215). The crystal must 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 PA0 and PA1 on the bottom side of the board (J207, J208)
