PIC24F08KL301-I/SS【PDF 146/260 页】IC MCU 16BIT 8KB FLASH 20-SSOP

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2011 Microchip Technology Inc.

DS31037B-page 23

PIC24F16KL402 FAMILY

2.4

ICSP Pins

The PGC and PGD pins are used for In-Circuit Serial

Programming (ICSP) and debugging purposes. It

is recommended to keep the trace length between the

ICSP connector and the ICSP pins on the device as

short as possible. If the ICSP connector is expected to

experience an ESD event, a series resistor is recom-

mended, with the value in the range of a few tens of

ohms, not to exceed 100.

Pull-up resistors, series diodes and capacitors on the

PGC and PGD pins are not recommended as they will

interfere with the programmer/debugger communica-

tions to the device. If such discrete components are an

application requirement, they should be removed from

the circuit during programming and debugging. Alter-

natively, refer to the AC/DC characteristics and timing

requirements information in the respective device

Flash programming specification for information on

capacitive loading limits, and pin input voltage high

(VIH) and input low (VIL) requirements.

For device emulation, ensure that the “Communication

Channel Select” (i.e., PGCx/PGDx pins), programmed

into the device, matches the physical connections for

the ICSP to the Microchip debugger/emulator tool.

For

information

available

Microchip

development tools connection requirements, refer to

Section 24.0 “Development Support”

2.5

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 9.0 “Oscillator Configuration”

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 cir-

cuit 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.

Layout suggestions are shown in Figure 2-3. In-line

packages may be handled with a single-sided layout

that completely encompasses the oscillator pins. With

fine-pitch packages, it is not always possible to com-

pletely surround the pins and components. A suitable

solution is to tie the broken guard sections to a mirrored

ground layer. In all cases, the guard trace(s) must be

returned to ground.

FIGURE 2-3:

SUGGESTED PLACEMENT

OF THE OSCILLATOR

CIRCUIT

In planning the application’s routing and I/O assign-

ments, ensure that adjacent port pins and other

signals, in close proximity to the oscillator, are benign

(i.e., free of high frequencies, short rise and fall times,

and other similar noise).

GND

OSC1

OSC2

T1OSO

T1OS I

Copper Pour

Primary Oscillator

Crystal

Timer1 Oscillator

Crystal

DEVICE PINS

Primary

Oscillator

T1 Oscillator: C1

T1 Oscillator: C2

(tied to ground)

Single-Sided and In-Line Layouts:

Fine-Pitch (Dual-Sided) Layouts:

GND

OSCO

OSCI

Bottom Layer

Copper Pour

Oscillator

Crystal

Top Layer Copper Pour

DEVICE PINS

(tied to ground)

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