PIC24FJ256GA110_10 Datasheet, PDF (254/330 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit, General Purpose Flash Microcontrollers with Peripheral Pin Select

PIC24FJ256GA110 FAMILY
25.4.2 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
separate block of erase and write-protected code is
needed, such as bootloader applications. Unlike
common boot block implementations, the specially pro-
tected segment in the PIC24FJ256GA110 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 Flash Configuration Word 3. Code
segment 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
unprogrammed (= 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 independently protect
the last page of program space, including the Flash Con-
figuration Words. If WPEND is set to protect the bottom
of program memory, programming WPCFG (= 0) pro-
tects the last page. This may be useful in circumstances
where write protection is needed for both a code
segment in the bottom of memory, as well as the Flash
Configuration Words.
The various options for segment code protection are
shown in Table 25-2.
25.4.3
CONFIGURATION REGISTER
PROTECTION
The Configuration registers are protected against
inadvertent or unwanted changes, or reads in two
ways. The primary protection method is the same as
that of the RP registers – shadow registers contain a
complimentary value which is constantly compared
with the actual value.
To safeguard against unpredictable events, Configura-
tion bit changes resulting from individual cell level
disruptions (such as ESD events) will cause a parity
error and trigger a device Reset.
The data for the Configuration registers is derived from
the Flash Configuration Words in program memory.
When the GCP bit is set, the source data for device
configuration is also protected as a consequence. Even
if General Segment protection is not enabled, the
device configuration can be protected by using the
appropriate code segment protection setting.
TABLE 25-2: SEGMENT CODE PROTECTION CONFIGURATION OPTIONS
Segment Configuration Bits
WPDIS WPEND WPCFG
Write/Erase Protection of Code Segment
1
x
x
No additional protection enabled; all program memory protection is configured
by GCP and GWRP
0
1
x
Addresses from the first address of code page, defined by WPFP<7:0> through
the end of implemented program memory (inclusive), are write/erase protected
including Flash Configuration Words
0
0
1
Address, 000000h through the last address of code page, defined by
WPFP<7:0> (inclusive), is protected
0
0
0
Address, 000000h through the last address of code page, defined by
WPFP<7:0> (inclusive) are write/erase protected and the last page is also
write/erase protected.
DS39905E-page 254
 2010 Microchip Technology Inc.