nm95hs02 National Semiconductor Corporation, nm95hs02 Datasheet - Page 2

• Manufacturer Part Number: nm95hs02
• Description: Hisec-tm High Security Rolling Code Generator
• Manufacturer: National Semiconductor Corporation

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General Characteristics
The NM95HS01 02HiSeC Generator was developed to
meet existing standards for rolling code-based security sys-
tems
Theft prevention systems typically involve user identification
and transmission of information at various distances from
the vehicle These Remote Keyless Entry (RKE) systems
are generally implemented with IR transmitters for short dis-
tances or RF transmitters for longer distances RF trans-
mission has become state of the art however the longer
distances involved require a much higher degree of security
since the possibility of signal interception is greatly in-
creased
These
NM95HS01 02 This generator is a small footprint low cur-
rent solution that supports both IR and RF transmission
The device is available in an 8-pin SO package with 2 key
switch inputs or a 14-pin SO package with 4 key switch
inputs
The proprietary coding scheme used generates a rolling
code based on 2
sures a high level of coding security for any RKE applica-
tion The NM95HS01 can be clocked with an RC circuit
while the NM95HS02 can be clocked with a crystal oscilla-
tor
General Device Operation
The Functional Block Diagram (Figure 1) shows the internal
elements of the code generating logic and program regis-
ters
The NM95HS01 02 HiSeC Generator achieves its high se-
curity level by combining the contents of several dynamic
data registers in a non-linear manner to generate an encod-
ed output Data in the registers is comprised of a mixture of
user programmable data factory programmable data and
randomized data This inherently random and separate data
is encrypted by clocking it through a non-linear logic block
and feeding part of the output back to produce a final coded
output with a high degree of linear complexity and correla-
tion immunity
The NM95HS01 02 incorporates 13 bytes of non-volatile
EEPROM memory which can be used to configure the de-
vice registers This memory is accessible to the user and
can be configured to the desired configuration then write-
disabled to prevent tampering
User programmable data includes 24 bits of the code block
a 24-bit key ID register and an 8-bit sync field register
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applications
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possible user combinations and en-
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Figure 2 shows a general operational block diagram of the
The 24-bit key ID register can be used to configure a large
number of unique keys each of which will produce a unique
encoded output bit stream The 24 bits in the code genera-
tor block are mixed with coded data
The output of this block is then fed into the 24- 36-bit buffer
register where the 40 bits are recombined to produce a 24-
or 36-bit output (a user option) The 8-bit sync field register
can be configured by the user to provide a pattern to facili-
tate synchronization between the transmitter and receiver
The details of the code block are available to customers
and exclusive algorithms are available and under contract
with National Call your local sales office for details
The HiSeC Generator is shipped with a standard algorithm
as a standard product with the configuration shown
NM95HS01 02 HiSeC Generator The 4 key switch inputs
shown use internal pull-up resistors and are suitable for
normally open single pole input switches connected to
ground The inputs are buffered by debounce logic which
repeatedly polls the inputs to determine if a key switch has
been asserted If any key switch input is seen as low for four
continuous 10 ms samples its associated output is set high
the HiSeC control logic is activated and a security code is
generated and transmitted
The timer block is used to set the key debounce time and
the IR or RF clock times These clock times are used as the
time base for the chosen bit coding format The timer block
is also used to generate the interframe pause time and the
timeout delay if these are enabled These parameters are
configured by the user in the 13-byte on-chip EEPROM ar-
ray
The NM95HS01 version of the device uses an RC network
to clock the CKI input pin The CKO LED pin is not required
for clocking but may be used for a visual indicator LED If
the NM95HS02 crystal oscillator version is used the device
is clocked using both the CKI and CKO pins If an LED is
used with this device it may be grounded through the
RFEN LED pin Either the CKO LED or the RFEN LED out-
put pins can provide the sink current needed to drive an
indicator LED The RFEN pin is active low during signal
transmission and is used to provide power to the RF circuit
only during transmission to increase battery life
The transmit output (TX) pin is a configurable logic level
output and is used to transmit the encoded bit stream An
on-chip power-on reset circuit is used to initialize the device
during power-up