Microchip Technology DM183021 Data Sheet

DS39616D-page 282

 2010 Microchip Technology Inc.

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 external writes to data EEPROM. The
CPU can continue to read and write data EEPROM
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 or
an external programmer.

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.

PIC18F2331/2431/4331/4431 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 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.

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 resources are not available for general use.

 shows which resources are required by the

background debugger.

To use the In-Circuit Debugger function of the micro-
controller, the design must implement In-Circuit Serial
Programming connections to MCLR/V

PP

, V

DD

, V

SS

,

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 LVP bit in Configuration Register 4L
(CONFIG4L<2>) enables Single-Supply ICSP
Programming. When LVP is enabled, the microcontroller
can be programmed without requiring high voltage being
applied to the MCLR/V

PP

 pin, but the RB5/PGM pin is

then dedicated to controlling Program mode entry and is
not available as a general purpose I/O pin.
LVP is enabled in erased devices.
While programming, using Single-Supply Program-
ming, V

DD

 is applied to the MCLR/V

PP

 pin as in normal

execution mode. To enter Programming mode, V

DD

 is

applied to the PGM pin. 

If Single-Supply ICSP Programming mode will not be
used, the LVP bit can be cleared and RB5/PGM
becomes available as the digital I/O pin RB5. The LVP
bit may be set or cleared only when using standard
high-voltage programming (V

IHH

 applied to the MCLR/

V

PP

 pin). Once LVP has been disabled, only the

standard high-voltage programming is available and
must be used to program the device. 
Memory that is not code-protected can be erased using
either a block erase, or erased row by row, then written
at any specified V

DD

. If code-protected memory is to be

erased, a block erase is required. If a block erase is to
be performed when using Single-Supply Programming,
the device must be supplied with V

DD 

of 4.5V to 5.5V. 

I/O pins:

RB6, RB7

Stack:

2 levels

Program Memory:

<1 Kbytes

Data Memory:

16 bytes

High-voltage programming is always
available, regardless of the state of the
LVP bit or the PGM pin, by applying V

IHH

to the MCLR pin.

When Single-Supply Programming is
enabled, the RB5 pin can no longer be
used as a general purpose I/O pin.

When LVP is enabled externally, pull the
PGM pin to V

SS

 to allow normal program

execution.