PIC24FJ128GA310 datasheet(345/406 Pages) MICROCHIP

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 2010-2011 Microchip Technology Inc.

DS39996F-page 345

PIC24FJ128GA310 FAMILY

29.4

Program Verification and

Code Protection

PIC24FJ128GA310 family devices provide two compli-

mentary methods to protect application code from

overwrites and erasures. These also help to protect the

device from inadvertent configuration changes during

run time.

29.4.1

GENERAL SEGMENT PROTECTION

For all devices in the PIC24FJ128GA310 family, the

on-chip program memory space is treated as a single

block, known as the General Segment (GS). Code pro-

tection for this block is controlled by one Configuration

bit, GCP. This bit inhibits external reads and writes to

the program memory space. It has no direct effect in

normal execution mode.

Write protection is controlled by the GWRP bit in the

Configuration Word. When GWRP is programmed to

‘0’, internal write and erase operations to program

memory are blocked.

29.4.2

CODE SEGMENT PROTECTION

In addition to global General Segment protection, a

separate subrange of the program memory space can

be individually protected against writes and erases.

This area can be used for many purposes where a sep-

arate block of write and erase-protected code is

needed, such as bootloader applications. Unlike

common boot block implementations, the specially

protected segment in the PIC24FJ128GA310 family

devices can be located by the user anywhere in the

program space and configured in a wide range of sizes.

Code segment protection provides an added level of

protection to a designated area of program memory by

disabling the NVM safety interlock whenever a write or

erase address falls within a specified range. It does not

override General Segment protection controlled by the

GCP or GWRP bits. For example, if GCP and GWRP

are enabled, enabling segmented code protection for

the bottom half of program memory does not undo

General Segment protection for the top half.

The size and type of protection for the segmented code

range are configured by the WPFPx, WPEND, WPCFG

and WPDIS bits in Configuration Word 3. Code seg-

ment protection is enabled by programming the WPDIS

bit (= 0). The WPFP bits specify the size of the segment

to be protected, by specifying the 512-word code page

that is the start or end of the protected segment. The

specified region is inclusive, therefore, this page will

also be protected.

The WPEND bit determines if the protected segment

uses the top or bottom of the program space as a

boundary. Programming WPEND (= 0) sets the bottom

of program memory (000000h) as the lower boundary

of the protected segment. Leaving WPEND unpro-

grammed (= 1) protects the specified page through the

last page of implemented program memory, including

the Configuration Word locations.

A separate bit, WPCFG, is used to protect the last page

of program space, including the Flash Configuration

Words. Programming WPCFG (= 0) protects the last

page in addition to the pages selected by the WPEND

and WPFP<6:0> bits setting. This is useful in circum-

stances where write protection is needed for both the

code segment in the bottom of the memory and the

Flash Configuration Words.

The various options for segment code protection are

shown in Table 29-2.

TABLE 29-2:

CODE SEGMENT PROTECTION CONFIGURATION OPTIONS

Segment Configuration Bits

Write/Erase Protection of Code Segment

WPDIS

WPEND

WPCFG

1xx

No additional protection is enabled; all program memory protection is configured

by GCP and GWRP.

01x

Addresses from the first address of the code page are defined by WPFP<7:0>

through the end of implemented program memory (inclusive); write/erase

protected, including Flash Configuration Words.

001

Address 000000h through the last address of the code page is defined by

WPFP<7:0> (inclusive); write/erase protected.

000

Address 000000h through the last address of code page is defined by

WPFP<7:0> (inclusive); write/erase protected and the last page, including Flash

Configuration Words, are write/erase protected.

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