Rainbow Electronics T89C51AC2 User Manual
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T89C51AC2
Rev. B – 19-Dec-01
Figure 15. Reading Procedure
9.3.8 Flash Protection from
Parallel Programming
The three lock bits in Hardware Security Byte (see "In-System Programming" section)
are programmed according to Table 11 provide different level of protection for the on-
chip code and data located in FM0 and FM1.
The only way to write this bits are the parallel mode. They are set by default to level 4
Table 11. 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.
FLASH Spaces
Reading
FLASH Spaces Mapping
FCON= 00000xx0b
Data Read
DPTR= Address
ACC= 0
Exec: MOVC A, @A+DPTR
Clear Mode
FCON = 00h
Program Lock Bits
Protection description
Security
level
LB0
LB1
LB2
1
U
U
U
No program lock features enabled. MOVC instruction executed from
external program memory returns non encrypted data.
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.
3
U
P
U
Same as 2, also verify through parallel programming interface is
disabled.
4
U
U
P
Same as 3, also external execution is disabled if code roll over beyond
7FFFh