PIC18F6520-I Datasheet, PDF (259/380 Pages) Micrel Semiconductor – 64/80-Pin High-Performance, 256 Kbit to 1 Mbit Enhanced Flash Microcontrollers with A/D

PIC18F6520/8520/6620/8620/6720/8720
23.4.2 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.
23.4.3 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.
23.5 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.
23.6 In-Circuit Serial Programming
PIC18FX520/X620/X720 microcontrollers can be seri-
ally programmed 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 manu-
facture 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.
Note:
When performing In-Circuit Serial
Programming, verify that power is con-
nected to all VDD and AVDD pins of the
microcontroller and that all VSS and AVSS
pins are grounded.
23.7 In-Circuit Debugger
When the DEBUG bit in the CONFIG4L Configuration
register 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. Table 23-4 shows which features are consumed
by the background debugger.
TABLE 23-4: DEBUGGER RESOURCES
I/O pins
RB6, RB7
Stack
2 levels
Program Memory
Last 576 bytes
Data Memory
Last 10 bytes
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.
23.8 Low-Voltage ICSP Programming
The LVP bit in the CONFIG4L Configuration register
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.
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 and should be
held low during normal operation.
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
programmed when programming is entered with VIHH
on MCLR/VPP.
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, the part may be
programmed at the normal operating voltage. This
means unique user IDs or user code can be
reprogrammed or added.
 2004 Microchip Technology Inc.
DS39609B-page 257