87C51F Intel Corporation, 87C51F Datasheet - Page 16

• Manufacturer Part Number: 87C51F
• Description: CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER
• Manufacturer: Intel Corporation

AUTOMOTIVE 87C51FA FB FC FC-20
EPROM Program Lock
The 87C51FA FB FC program lock system when
programmed protects the onboard program against
software piracy
The 87C51FA FB FC has a 3-level program lock
system and a 64-byte encryption array Since this is
an EPROM device all locations are user program-
mable See Table 4
Program Lock Bits
The 87C51FA FB FC has 3 programmable lock bits
that when programmed according to Table 4 will
provide different levels of protection for the on-chip
code and data
Erasing the EPROM also erases the encryption ar-
ray and the program lock bits returning the part to
full functionality
Any other combination of the lock bits is not defined
16
1
2
3
4
Program Lock Bits
LB1
U
P
P
P
LB2
U
U
P
P
LB3
U
U
U
P
No Program Lock features enabled (Code verify will still be encrypted by the
Encryption Array if programmed )
MOVC instructions executed from external program memory are disabled
from fetching code bytes from internal memory EA is sampled and latched on
Reset and further programming of the EPROM is disabled
Same as 2 also verify is disabled
Same as 3 also external execution is disabled
Table 4 Program Lock Bits and the Features
Encryption Array
Within the EPROM array are 64 bytes of Encryption
Array that are initially unprogrammed (all 1’s) Every
time that a byte is addressed during a verify 6 ad-
dress lines are used to select a byte of the Encryp-
tion Array This byte is then exclusive-NOR’ed
(XNOR) with the code byte creating an Encryption
Verify byte The algorithm with the array in the un-
programmed state (all 1’s) will return the code in it’s
original unmodified form For programming the En-
cryption Array refer to Table 3 (EPROM Program-
ming Mode)
Reading the Signature Bytes
The 87C51FA FB FC has 3 signature bytes in loca-
tions 30H 31H and 60H To read these bytes follow
the procedure for EPROM verify but activate the
control lines provided in Table 3 for Read Signature
Byte
Location
Protection Type
30H
31H
60H
60H
e
e
e
e
89H
58H
FBH (for an FB part)
FCH (for an FC part)