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8XC51FX Datasheet(PDF) 18 Page - Intel Corporation

No. de Pieza. 8XC51FX
Descripción  CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLERS
Descarga  20 Pages
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Fabricante  INTEL [Intel Corporation]
Página de inicio  http://www.intel.com
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8XC51FX Datasheet(HTML) 18 Page - Intel Corporation

 
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8XC51FX
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 its
original unmodified form For programming the En-
cryption Array refer to Table 4 (Programming the
EPROM)
When using the encryption array one important fac-
tor needs to be considered If a code byte has the
value 0FFH verifying the byte will produce the en-
cryption byte value lf a large block (l64 bytes) of
code is left unprogrammed a verification routine will
display the contents of the encryption array For this
reason all unused code bytes should be pro-
grammed with some value other than 0FFH and not
all of them the same value This will ensure maxi-
mum program protection
Program Lock Bits
The 87C51FX has 3 programmable lock bits that
when programmed according to Table 5 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
Reading the Signature Bytes
The 87C51FX has 3 signature bytes in locations
30H 31H and 60H The 83C51FA has 2 signature
bytes in locations 30H and 31H To read these bytes
follow the procedure for EPROM verify but activate
the control lines provided in Table 4 for Read Signa-
ture Byte
Location
Device
Contents
30H
All
89H
31H
All
58H
60H
83C51FA
7AHFAH
87C51FA
FAH
83C51FB
7BHFBH
87C51FB
FBH
83C51FC
7CHFCH
87C51FC
FCH
Erasure Characteristics (Windowed
Packages Only)
Erasure of the EPROM begins to occur when the
chip is exposed to light with wavelength shorter than
approximately 4000 Angstroms Since sunlight and
fluorescent lighting have wavelengths in this range
exposure to these light sources over an extended
time (about 1 week in sunlight or 3 years in room-
level fluorescent lighting) could cause inadvertent
erasure If an application subjects the device to this
type of exposure it is suggested that an opaque la-
bel 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-seccm Exposing the
EPROM to an ultraviolet lamp of 12000 mWcm rat-
ing for 30 minutes at a distance of about 1 inch
should be sufficient
Erasure leaves all the EPROM Cells in a 1’s state
18


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