PIC18F2431T-I/ML【PDF 40/119 页】IC MCU FLASH 8KX16 28QFN

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2010 Microchip Technology Inc.

DS39616D-page 27

PIC18F2331/2431/4331/4431

2.3

Master Clear (MCLR) Pin

The MCLR pin provides two specific device

functions: Device Reset, and Device Programming

and Debugging. If programming and debugging are

not required in the end application, a direct

connection to VDD may be all that is required. The

addition of other components, to help increase the

application’s resistance to spurious Resets from

voltage

sags,

may

beneficial.

typical

configuration is shown in Figure 2-1. Other circuit

designs may be implemented, depending on the

application’s requirements.

During programming and debugging, the resistance

and capacitance that can be added to the pin must be

considered. Device programmers and debuggers drive

the MCLR pin. Consequently, specific voltage levels

(VIH and VIL) and fast signal transitions must not be

adversely affected. Therefore, specific values of R1

and C1 will need to be adjusted based on the

application and PCB requirements. For example, it is

recommended that the capacitor, C1, be isolated from

the MCLR pin during programming and debugging

operations by using a jumper (Figure 2-2). The jumper

is replaced for normal run-time operations.

Any components associated with the MCLR pin

should be placed within 0.25 inch (6 mm) of the pin.

FIGURE 2-2:

EXAMPLE OF MCLR PIN

CONNECTIONS

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 25.0 “Development Support”

Note 1:

10 k is recommended. A suggested

starting value is 10 k

. Ensure that the

MCLR pin VIH and VIL specifications are met.

470 will limit any current flowing into

MCLR from the external capacitor, C, in the

event of MCLR pin breakdown, due to

Electrostatic Discharge (ESD) or Electrical

Overstress (EOS). Ensure that the MCLR pin

VIH and VIL specifications are met.

VDD

MCLR

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