PIC18F258 Datasheet, PDF (277/384 Pages) Microchip Technology – High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN

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 regis-
ters. 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 des-
ignated 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 feature
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.
PIC18FXX8
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 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 pro-
gramming 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, provided the LVP bit is set.
The LVP bit defaults to a (‘1’) from the factory.
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.
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 pro-
grammed 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 avail-
able and only High Voltage Programming mode can be
used to program the device.
When using Low Voltage ICSP, the part must be sup-
plied 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 off-state. For all other cases of Low Volt-
age ICSP, the part may be programmed at the normal
operating voltage. This means unique user IDs, or user
code can be reprogrammed or added.
 2002 Microchip Technology Inc.
Preliminary
DS41159B-page 275