5.3 32.768 kHz Crystal Footprint

The PIC32CM Px DIP-28 Curiosity Nano Board has a 32.768 kHz crystal footprint. The crystal is not connected to the target device by default, because the GPIO pins are routed to the edge connector.

Figure 5-3. 32.768 kHz Crystal Block Diagram
Table 5-3. Crystal Connections
Device PinDescriptionDefault Connection
PA24Crystal output, XTAL32K1Edge connector
PA25Crystal input, XTAL32K2
Warning: Always disconnect the board from all power sources before making any hardware modifications.
How to Connect a Crystal to the Target Device
  1. Disconnect the two I/O lines routed to the edge connector by cutting the two cut straps, J115 and J116, on the bottom side of the board.
  2. Connect the two I/O lines to the crystal by soldering a blob onto each circular solder point, J121 and J122, on the top side of the board.
Figure 5-4. 32.768 kHz Crystal Overview
Info: The 0Ω series resistor, R113, may be replaced by any suitable resistor to limit the drive strength of the crystals. If no resistor is required, leave the resistor in place.

The 32.768 kHz crystal has a cut strap (J124), that can be used to measure the oscillator safety factor. This is done by cutting the strap and adding a 0402 SMD resistor across it. The Microchip application note AN2648 contains more information about oscillator allowance and safety factors.