Rev. 1.1
137
C8051F410/1/2/3
16.2. Non-volatile Data Storage
The Flash memory can be used for non-volatile data storage as well as program code. This allows data
such as calibration coefficients to be calculated and stored at run time. Data is written using the MOVX
write instruction and read using the MOVC instruction. Note: MOVX read instructions always target XRAM.
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 the example below for an C8051F410.
Access limit set
according to the Flash
security lock byte
0x0000
0x3FFF
Lock Byte
Reserved
0x3FFE
0x4000
Flash memory organized
in 512-byte pages
0x3E00
Unlocked Flash Pages
Locked when any
other Flash pages are
locked
0x0000
0x7DFF
Lock Byte
Reserved
0x7DFE
0x7E00
0x7C00
Unlocked Flash Pages
C8051F410/1
C8051F412/3
Figure 16.1. Flash Program Memory Map
Security Lock Byte:
11111101b
1’s Complement:
00000010b
Flash pages locked:
3 (First two Flash pages + Lock Byte Page)
Addresses locked:
0x0000 to 0x03FF (first two Flash pages) and
0x7C00 to 0x7DFF (Lock Byte Page)