PIC18F23K20 Datasheet, PDF (303/420 Pages) Microchip Technology – 28/40/44-Pin Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

PIC18F2XK20/4XK20
23.3.1 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 CPn bits have no direct
effect. CPn bits inhibit external reads and writes. A block
of user memory may be protected from table writes if the
WRTn Configuration bit is ‘0’. The EBTRn bits control
table reads. For a block of user memory with the EBTRn
bit cleared 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.
Figures 23-3 through 23-5 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 pro-
tection 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 or an external
programmer.
FIGURE 23-3:
TABLE WRITE (WRTn) DISALLOWED
Register Values
TBLPTR = 0008FFh
Program Memory
000000h
0007FFh
000800h
PC = 001FFEh
PC = 005FFEh
TBLWT*
TBLWT*
001FFFh
002000h
003FFFh
004000h
005FFFh
006000h
007FFFh
Results: All table writes disabled to Blockn whenever WRTn = 0.
Configuration Bit Settings
WRTB, EBTRB = 11
WRT0, EBTR0 = 01
WRT1, EBTR1 = 11
WRT2, EBTR2 = 11
WRT3, EBTR3 = 11
© 2007 Microchip Technology Inc.
Advance Information
DS41303B-page 301