Datasheet

52
AT89C51AC3
4383D–8051–02/08
Table 17. Program Lock Bit
Program Lock bits
U: unprogrammed
P: programmed
WARNING: Security level 2 and 3 should only be programmed after Flash and Core
verification.
Program Lock Bits
Protection Description
Security
level
LB0 LB1 LB2
1 U U U No program lock features enabled.
2 P U U
MOVC instruction executed from external program memory are
disabled from fetching code bytes from internal memory, EA is sampled
and latched on reset, and further parallel programming of the Flash is
disabled.
ISP and software programming with API are still allowed.
Writing EEprom Data from external parallel programmer is disabled but
still allowed from internal code execution.
3 U P U
Same as 2, also verify through parallel programming interface is
disabled.
Writing And Reading EEPROM Data from external parallel programmer
is disabled but still allowed from internal code execution..
4 U U P Same as 3, also external execution is disabled