PIC32MX795F512LT-80ISLASHPF datasheet(46/256 Pages) MICROCHIP

46 / 256 page

PIC32MX5XX/6XX/7XX

DS61156G-page 46

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

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.

Main Oscillator

Guard Ring

Guard Trace

Secondary

Oscillator

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