PIC18F2450_08 Datasheet, PDF (211/324 Pages) Microchip Technology – 28/40/44-Pin, High-Performance, 12 MIPS, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

PIC18F2450/4450
18.5.1 PROGRAM MEMORY
CODE PROTECTION
The program memory may be read to or written from
any location using the table read and table write
instructions. The device ID may be read with table
reads. The Configuration registers may be read and
written with the table read and table write instructions.
In normal execution mode, the CPx bits have no direct
effect. CPx bits inhibit external reads and writes. A
block of user memory may be protected from table
writes if the WRTx Configuration bit is ‘0’. The EBTRx
bits control table reads. For a block of user memory
with the EBTRx bit set to ‘0’, a table read instruction
that executes from within that block is allowed to read.
A table read instruction that executes from a location
outside of that block is not allowed to read and will
result in reading ‘0’s. Figure 18-6 through Figure 18-8
illustrate table write and table read protection.
Note:
Code protection bits may only be written to
a ‘0’ from a ‘1’ state. It is not possible to
write a ‘1’ to a bit in the ‘0’ state. Code
protection bits are only set to ‘1’ by a full
Chip Erase or Block Erase function. The
full Chip Erase and Block Erase functions
can only be initiated via ICSP operation or
an external programmer.
FIGURE 18-6:
TABLE WRITE (WRTx) DISALLOWED
Register Values
TBLPTR = 0008FFh
PC = 001FFEh
Program Memory
000000h
0007FFh
000FFFh
001000h
TBLWT*
001FFFh
002000h
003FFFh
Configuration Bit Settings
WRTB, EBTRB = 11
WRT0, EBTR0 = 01
WRT1, EBTR1 = 11
WRT2, EBTR2 = 11
Results: All table writes disabled to Blockn whenever WRTx = 0.
WRT3, EBTR3 = 11
© 2008 Microchip Technology Inc.
DS39760D-page 209