PIC18LF4331 datasheet(280/392 Pages) MICROCHIP

280 / 392 page

PIC18F2331/2431/4331/4431

DS39616D-page 280

 2010 Microchip Technology Inc.

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 instruc-

tion 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.

FIGURE 23-6:

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

0007FFh

000800h

000FFFh

001000h

0017FFh

001800h

001FFFh

WRTB, EBTRB = 11

WRT0, EBTR0 = 01

WRT1, EBTR1 = 11

WRT2, EBTR2 = 11

WRT3, EBTR3 = 11

TBLWT *

TBLPTR = 0002FFh

PC = 0007FEh

TBLWT *

PC = 0017FEh

Program Memory

Configuration Bit Settings

Results:

All table writes are disabled to Blockn whenever WRTn = 0

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