C8051F336/7/8/9
16.3. 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
software 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. The Flash security
mechanism allows the user to lock n 512-byte Flash pages, starting at page 0 (addresses 0x0000 to
0x01FF), where n is the 1’s complement number represented by the Security Lock Byte. Note that 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’). See example in Figure 16.1.
Reserved Area
Lock Byte
Locked when
any other FLASH
pages are locked
Lock Byte Page
Unlocked FLASH Pages
Access limit set
according to the
FLASH security
lock byte
Locked Flash Pages
Security Lock Byte:
1s Complement:
11111101b
00000010b
Flash pages locked:
3 (First two Flash pages + Lock Byte Page)
Figure 16.1. Flash Program Memory Map
100
Rev. 0.2
SILICON [ SILICON ]
