The PIC16F17576 Curiosity Nano Board has a 32.768 kHz crystal
mounted (VMK3-9002-32K7680000). By default, the crystal is connected to the
PIC16F17576. The GPIO pins are disconnected from the edge
connector to avoid contention and to remove excessive capacitance on the lines. Disconnecting
the crystal from the PIC16F17576 and using the pins for other
purposes requires a few hardware modifications.
Figure 4-1. 32.768 kHz Crystal Block Diagram
Warning: Disconnect the USB or any
external power supply before doing any hardware modifications.
How to disconnect the crystal from the PIC16F17576:
Disconnect the two I/O lines routed to
crystal by cutting the two cut straps on the top side of the board, J109 and J110.
Connect the two I/O lines to the edge
connector by soldering a blob to each circular solder point at the bottom of the board,
J107 and J108. These are marked RC1 and RC0 in the silkscreen.
Figure 4-2. 32.768 kHz Crystal Overview
Info: The 0Ω series resistor, R105, 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 uses a cut strap (J111) to measure the oscillator safety factor (this
is done by cutting the strap and adding a 0402 SMD resistor across it). The AN2648 application note from Microchip contains more information
about oscillator allowance and safety factors.
