C8051F99X_10 Datasheet, PDF (151/322 Pages) Silicon Laboratories – Ultra Low Power, 8-2 kB Flash, Capacitive Sensing MCU

C8051F99x-C8051F98x
14.3. Security Options
The CIP-51 provides security options to protect the Flash memory from inadvertent modification by soft-
ware as well as to prevent the viewing of proprietary program code and constants. The Program Store
Write Enable (bit PSWE in register PSCTL) and the Program Store Erase Enable (bit PSEE in register
PSCTL) bits protect the Flash memory from accidental modification by software. PSWE must be explicitly
set to 1 before software can modify the Flash memory; both PSWE and PSEE must be set to 1 before soft-
ware can erase Flash memory. Additional security features prevent proprietary program code and data
constants from being read or altered across the C2 interface.
A Security Lock Byte located at the last byte of Flash user space offers protection of the Flash program
memory from access (reads, writes, or erases) by unprotected code or the C2 interface. See Section
“10. Memory Organization” on page 127 for the location of the security byte. The Flash security mecha-
nism allows the user to lock n 512-byte Flash pages, starting at page 0 (addresses 0x0000 to 0x01FF),
where n is the 1s complement number represented by the Security Lock Byte. The page containing the
Flash Security Lock Byte is unlocked when no other Flash pages are locked (all bits of the Lock
Byte are 1) and locked when any other Flash pages are locked (any bit of the Lock Byte is 0).
Security Lock Byte:
ones Complement:
Flash pages locked:
1111 1011b
0000 0100b
5 (First four Flash pages + Lock Byte Page)
8KB Flash Device
4 or 2 KB Flash Device
Reserved
Lock Byte
Lock Byte Page
Unlocked Flash Pages
Locked when
any other
Flash pages
are locked
Access limit
set according
to the Flash
security lock
byte
Reserved
Lock Byte
Lock Byte Page
Unlocked Flash Pages
Figure 14.1. Flash Program Memory Map (8 kB and smaller devices)
The level of Flash security depends on the Flash access method. The three Flash access methods that
can be restricted are reads, writes, and erases from the C2 debug interface, user firmware executing on
unlocked pages, and user firmware executing on locked pages. Table 14.1 summarizes the Flash security
features of the C8051F99x-C8051F98x devices.
Rev. 1.0
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