PIC18F44J10 datasheet(28/368 Pages) MICROCHIP

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PIC18F45J10 FAMILY

DS39682E-page 26

2.6

External Oscillator Pins

Many microcontrollers have options for at least two

oscillators: a high-frequency primary oscillator and a

low-frequency

secondary

oscillator

(refer

Section 3.0 “Oscillator Configurations”

for details).

The oscillator circuit should be placed on the same

side of the board as the device. Place the oscillator

circuit close to the respective oscillator pins with no

more than 0.5 inch (12 mm) between the circuit

components and the pins. 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 it 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 shown in Figure 2-4.

For additional information and design guidance on

oscillator circuits, please refer to these Microchip

Application Notes, available at the corporate web site

(www.microchip.com):

• AN826, “Crystal Oscillator Basics and Crystal

Selection for rfPIC™ and PICmicro® Devices”

• AN849, “Basic PICmicro® Oscillator Design”

• AN943, “Practical PICmicro® Oscillator Analysis

and Design”

• AN949, “Making Your Oscillator Work”

FIGURE 2-4:

SUGGESTED PLACEMENT

OF THE OSCILLATOR

CIRCUIT

2.7

Unused I/Os

Unused I/O pins should be configured as outputs and

driven to a logic low state. Alternatively, connect a 1 kΩ

to 10 kΩ resistor to VSS on unused pins and drive the

output to logic low.

Main Oscillator

Guard Ring

Guard Trace

Secondary

Oscillator

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