PIC18F4321 Datasheet, PDF (273/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

23.5.2 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 internal and external writes to data
EEPROM. The CPU can always read data EEPROM
under normal operation, regardless of the protection bit
settings.
23.5.3 CONFIGURATION REGISTER
PROTECTION
The Configuration registers can be write-protected.
The WRTC bit controls protection of the Configuration
registers. In normal execution mode, the WRTC bit is
readable only. WRTC can only be written via ICSP
operation or an external programmer.
23.6 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 both readable and writable 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.
23.7 In-Circuit Serial Programming
PIC18F4321 family microcontrollers can be serially
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 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.
23.8 In-Circuit Debugger
When the DEBUG Configuration bit 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 resources are not available
for general use. Table 23-4 shows which resources are
required by the background debugger.
TABLE 23-4: DEBUGGER RESOURCES
I/O pins:
RB6, RB7
Stack:
2 levels
Program Memory:
512 bytes
Data Memory:
10 bytes
PIC18F4321 FAMILY
To use the In-Circuit Debugger function of the micro-
controller, the design must implement In-Circuit Serial
Programming connections to MCLR/VPP/RE3, VDD,
VSS, RB7 and RB6. This will interface to the In-Circuit
Debugger module available from Microchip or one of
the third party development tool companies.
23.9 Special ICPORT Features
(44-Pin TQFP Packages Only)
Under specific circumstances, the No Connect (NC)
pins of PIC18F4221/4321 devices in 44-pin TQFP
packages can provide additional functionality. These
features are controlled by device Configuration bits and
are available only in this package type and pin count.
23.9.1 DEDICATED ICD/ICSP PORT
The 44-pin TQFP devices can use NC pins to provide
an alternate port for In-Circuit Debugging (ICD) and In-
Circuit Serial Programming (ICSP). These pins are
collectively known as the dedicated ICSP/ICD port,
since they are not shared with any other function of the
device.
When implemented, the dedicated port activates three
NC pins to provide an alternate device Reset, data and
clock ports. None of these ports overlap with standard
I/O pins, making the I/O pins available to the user’s
application.
The dedicated ICSP/ICD port is enabled by setting the
ICPRT Configuration bit. The port functions the same
way as the legacy ICSP/ICD port on RB6/RB7.
Table 23-5 identifies the functionally equivalent pins for
ICSP and ICD purposes.
TABLE 23-5: EQUIVALENT PINS FOR
LEGACY AND DEDICATED
ICD/ICSP™ PORTS
Pin Name
Legacy
Port
Dedicated
Port
Pin
Type
Pin Function
MCLR/VPP/ NC/ICRST/
RE3
ICVPP
P Device Reset and
Programming
Enable
RB6/KBI2/ NC/ICCK/
PGC
ICPGC
I Serial Clock
RB7/KBI3/ NC/ICDT/
PGD
ICPGD
I/O Serial Data
Legend: I = Input, O = Output, P = Power
© 2007 Microchip Technology Inc.
Preliminary
DS39689E-page 271