PIC18F258-ESLASHLSQTP datasheet(279/402 Pages) MICROCHIP

279 / 402 page

DS41159E-page 277

PIC18FXX8

24.4.1

PROGRAM MEMORY

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.

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.

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.

000000h

0001FFh

000200h

001FFFh

002000h

003FFFh

004000h

005FFFh

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

Program Memory

Configuration Bit Settings

Results: All table writes disabled to Blockn whenever WRTn = 0.

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