Datasheet

 2011-2012 Microchip Technology Inc. Preliminary DS61168E-page 29
PIC32MX1XX/2XX
2.7 External Oscillator Pins
Many MCUs have options for at least two oscillators: a
high-frequency primary oscillator and a low-frequency
secondary oscillator (refer to Section 8.0 “Oscillator
Configuration” for details).
The oscillator circuit should be placed on the same side
of the board as the device. Also, place the oscillator cir-
cuit close to the respective oscillator pins, not exceed-
ing one-half inch (12 mm) distance between them. The
load capacitors should be placed next to the oscillator
itself, on the same side of the board. Use a grounded
copper pour around the oscillator circuit to isolate them
from surrounding circuits. The grounded copper pour
should be routed directly to the MCU ground. Do not
run any signal traces or power traces inside the ground
pour. Also, if using a two-sided board, avoid any traces
on the other side of the board where the crystal is
placed. A suggested layout is illustrated in Figure 2-3.
FIGURE 2-3: SUGGESTED OSCILLATOR
CIRCUIT PLACEMENT
2.8 Unused I/Os
Unused I/O pins should not be allowed to float as
inputs. They can be configured as outputs and driven
to a logic-low state.
Alternatively, inputs can be reserved by connecting the
pin to V
SS through a 1k to 10k resistor and configuring
the pin as an input.
Main Oscillator
Guard Ring
Guard Trace
Secondary
Oscillator