Microchip Technology DM164134 数据表
© 2006 Microchip Technology Inc.
DS41159E-page 277
PIC18FXX8
24.4.1
PROGRAM MEMORY
CODE PROTECTION
CODE PROTECTION
The user memory may be read to or written from any
location using the table read and table write instruc-
tions. 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.
location using the table read and table write instruc-
tions. 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 user 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 24-4 through 24-6
illustrate table write and table read protection.
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 24-4 through 24-6
illustrate table write and table read protection.
FIGURE 24-4:
TABLE WRITE (WRTn) DISALLOWED
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.
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.
000000h
0001FFh
000200h
000200h
001FFFh
002000h
002000h
003FFFh
004000h
004000h
005FFFh
006000h
006000h
007FFFh
WRTB, EBTRB = 11
WRT0, EBTR0 = 01
WRT1, EBTR1 = 11
WRT2, EBTR2 = 11
WRT3, EBTR3 = 11
TBLWT *
TBLPTR = 000FFF
PC = 001FFE
TBLWT *
PC = 004FFE
Register Values
Program Memory
Configuration Bit Settings
Results: All table writes disabled to Blockn whenever WRTn = 0.