PIC18F2220_07 Datasheet, PDF (254/386 Pages) Microchip Technology – 28/40/44-Pin High-Performance, Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

PIC18F2220/2320/4220/4320
23.5.1 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 instruction that executes from a location
outside of that block is not allowed to read and will
result in reading ‘0’s. Figures 23-6 through 23-8
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 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 23-6:
TABLE WRITE (WRTn) DISALLOWED
Register Values
TBLPTR = 0002FFh
Program Memory
000000h
0001FFh
000200h
PC = 0007FEh
PC = 0017FEh
TBLWT *
0007FFh
000800h
TBLWT *
000FFFh
001000h
0017FFh
001800h
001FFFh
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
DS39599F-page 252
© 2007 Microchip Technology Inc.