PIC32MX5XX_11 Datasheet, PDF (46/256 Pages) Microchip Technology – High-Performance, USB, CAN and Ethernet 32-bit Flash Microcontrollers

PIC32MX5XX/6XX/7XX
2.8 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
Oscillator
Secondary
Guard Trace
Guard Ring
Main Oscillator
2.9 Configuration of Analog and
Digital Pins During ICSP
Operations
If MPLAB ICD 2, ICD 3 or REAL ICE is selected as
a debugger, it automatically initializes all of the
Analog-to-Digital input pins (ANx) as “digital” pins by
setting all bits in the ADPCFG register.
The bits in this register that correspond to the Analog-
to-Digital pins that are initialized by MPLAB ICD 2, ICD
3 or REAL ICE, must not be cleared by the user
application firmware; otherwise, communication errors
will result between the debugger and the device.
If your application needs to use certain ADC pins as
analog input pins during the debug session, the user
application must clear the corresponding bits in the
ADPCFG register during initialization of the ADC
module.
When MPLAB ICD 2, ICD 3 or REAL ICE is used as a
programmer, the user application firmware must cor-
rectly configure the ADPCFG register. Automatic initial-
ization of this register is only done during debugger
operation. Failure to correctly configure the register(s)
will result in all ADC pins being recognized as analog
input pins, resulting in the port value being read as a
logic ‘0’, which may affect user application functionality.
2.10 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 VSS through a 1k to 10k resistor and configuring
the pin as an input.
DS61156G-page 46
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