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Rev. 0.5 111
C8051F340/1/2/3/4/5/6/7
12.2. 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.
12.3. 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 also locked when any other Flash pages are locked. See
example below.
Table 12.1. Flash Electrical Characteristics
Parameter Conditions Min Typ Max Units
Flash Size
C8051F340/2/4/6*
C8051F341/3/5/7
65536*
32768
Bytes
Bytes
Endurance 20k 100k Erase/Write
Erase Cycle Time 25 MHz System Clock 10 15 20 ms
Write Cycle Time 25 MHz System Clock 40 55 70 µs
*Note: 1024 bytes at location 0xFC00 to 0xFFFF are reserved.
Security Lock Byte: 11111101b
1’s Complement: 00000010b
Flash pages locked: 3 (2 + Flash Lock Byte Page)
Addresses locked:
First two pages of Flash: 0x0000 to 0x03FF
Flash Lock Byte Page: (0xFA00 to 0xFBFF for 64k devices; 0x7E00 to
0x7FFF for 32k devices)