PIC18F2331_07 Datasheet, PDF (288/400 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
22.5.1 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 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 set to ‘0’, a table read instruction that executes from
within that block is allowed to read. A table read instruc-
tion that executes from a location outside of that block is
not allowed to read, and will result in reading ‘0’s.
Figures 22-6 through 22-8 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 or an external
programmer.
FIGURE 22-6:
TABLE WRITE (WRTn) DISALLOWED
Register Values
TBLPTR = 0002FFh
PC = 0007FEh
PC = 0017FEh
Program Memory
000000h
0001FFh
000200h
TBLWT *
0007FFh
000800h
TBLWT *
000FFFh
001000h
0017FFh
001800h
001FFFh
Configuration Bit Settings
WRTB, EBTRB = 11
WRT0, EBTR0 = 01
WRT1, EBTR1 = 11
WRT2, EBTR2 = 11
WRT3, EBTR3 = 11
Results: All table writes disabled to Blockn whenever WRTn = 0.
DS39616C-page 286
Preliminary
© 2007 Microchip Technology Inc.