PIC18F258-ESLASHLSQTP datasheet(281/402 Pages) MICROCHIP

281 / 402 page

DS41159E-page 279

PIC18FXX8

24.4.2

DATA EEPROM

CODE PROTECTION

The entire data EEPROM is protected from external

reads and writes by two bits: CPD and WRTD. CPD

inhibits external reads and writes of data EEPROM.

WRTD inhibits external writes to data EEPROM. The

CPU can continue to read and write data EEPROM

regardless of the protection bit settings.

24.4.3

CONFIGURATION REGISTER

PROTECTION

The Configuration registers can be write-protected.

The WRTC bit controls protection of the Configuration

registers. In user mode, the WRTC bit is readable only.

WRTC can only be written via ICSP or an external

programmer.

24.5

ID Locations

Eight

memory

locations

(200000h-200007h)

are

designated as ID locations where the user can store

checksum or other code identification numbers. These

locations are accessible during normal execution

through the TBLRD and TBLWT instructions or during

program/verify. The ID locations can be read when the

device is code-protected.

24.6

In-Circuit Serial Programming

PIC18FXXX microcontrollers can be serially pro-

grammed while in the end application circuit. This is

simply done with two lines for clock and data and three

other lines for power, ground and the programming

voltage. This allows customers to manufacture boards

with unprogrammed devices and then program the

microcontroller just before shipping the product. This

also allows the most recent firmware or a custom

firmware to be programmed.

24.7

In-Circuit Debugger

When the DEBUG bit in Configuration register,

CONFIG4L, is programmed to a ‘0’, the In-Circuit

Debugger functionality is enabled. This function allows

simple

debugging

functions

when

used

with

MPLAB® IDE. When the microcontroller has this fea-

ture enabled, some of the resources are not available

for general use. Resources used include 2 I/O pins,

stack locations, program memory and data memory.

For more information on the resources required, see

the User’s Guide for the In-Circuit Debugger you are

using.

To use the In-Circuit Debugger function of the micro-

controller, the design must implement In-Circuit Serial

Programming connections to MCLR/VPP, VDD, GND,

RB7 and RB6. This will interface to the In-Circuit

Debugger module available from Microchip or one of

the third party development tool companies. The

Microchip In-Circuit Debugger (ICD) used with the

PIC18FXXX microcontrollers is the MPLAB® ICD 2.

24.8

Low-Voltage ICSP Programming

The LVP bit in Configuration register, CONFIG4L,

enables Low-Voltage ICSP Programming. This mode

allows the microcontroller to be programmed via ICSP

using a VDD source in the operating voltage range. This

only means that VPP does not have to be brought to

VIHH but can instead be left at the normal operating

voltage. In this mode, the RB5/PGM pin is dedicated to

the programming function and ceases to be a general

purpose I/O pin. During programming, VDD is applied to

the MCLR/VPP pin. To enter Programming mode, VDD

must be applied to the RB5/PGM pin, provided the LVP

bit is set. The LVP bit defaults to a (‘1’) from the factory.

If Low-Voltage Programming mode is not used, the LVP

bit can be programmed to a ‘0’ and RB5/PGM becomes

a digital I/O pin. However, the LVP bit may only be

programmed when programming is entered with VIHH

on MCLR/VPP. The LVP bit can only be charged when

using high voltage on MCLR.

It should be noted that once the LVP bit is programmed

to ‘0’, only the High-Voltage Programming mode is

available and only High-Voltage Programming mode

can be used to program the device.

When using Low-Voltage ICSP Programming, the part

must be supplied 4.5V to 5.5V if a bulk erase will be

executed. This includes reprogramming of the code-

protect bits from an ON state to an OFF state. For all

other cases of Low-Voltage ICSP Programming, the

part may be programmed at the normal operating

voltage. This means unique user IDs or user code can

be reprogrammed or added.

Note 1: The High-Voltage Programming mode is

always available, regardless of the state

of the LVP bit, by applying VIHH to the

MCLR pin.

2: While in Low-Voltage ICSP mode, the

RB5 pin can no longer be used as a

general purpose I/O pin.

3: When using Low-Voltage ICSP Program-

ming (LVP) and the pull-ups on PORTB

are enabled, bit 5 in the TRISB register

must be cleared to disable the pull-up on

RB5 and ensure the proper operation of

the device.

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