Datasheet

© 2006 Microchip Technology Inc. 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 V
DD source in the operating voltage range. This
only means that V
PP does not have to be brought to
V
IHH 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, V
DD 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 V
IHH
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.