87C51 Intel Corporation, 87C51 Datasheet - Page 19

• Manufacturer Part Number: 87C51
• Description: CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER
• Manufacturer: Intel Corporation

Program Lock Bits
The 87C51 has 3 programmable lock bits that when
programmed according to Table 5 will provide differ-
ent 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
Reading the Signature Bytes
The 87C51 and 80C51BH have 3 signature bytes in
locations 30H 31H and 60H To read these bytes
follow the procedure for EPROM verify but activate
the control lines provided in Table 4 for Read Signa-
ture Byte
1
2
3
4
Location
Program Lock Bits
30H
31H
60H
LB1
U
P
P
P
LB2
U
U
P
P
80C51BH
Device
LB3
87C51
U
U
U
P
All
All
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 5 Program Lock Bits and the Features
Contents
89H
58H
51H
11H
Erasure Characteristics
(Windowed Devices Only)
Erasure of the EPROM begins to occur when the
chip is exposed to light with wavelengths shorter
than approximately 4 000 Angstroms Since sunlight
and fluorescent lighting have wavelengths in this
range exposure to these light sources over an ex-
tended time (about 1 week in sunlight or 3 years in
room level fluorescent lighting) could cause inadver-
tent erasure If an application subjects the device to
this type of exposure it is suggested that an opaque
label be placed over the window
The recommended erasure procedure is exposure
to ultraviolet light (at 2537 Angstroms) to an integrat-
ed dose of at least 15 W-sec cm
EPROM to an ultraviolet lamp of 12 000
rating for 30 minutes at a distance of about 1 inch
should be sufficient
Erasure leaves the array in an all 1’s state
Protection Type
87C51 80C51BH 80C31BH
2
Exposing the
W cm
19
2