NM95HS02EN datasheet(2/20 Pages) NSC

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General Characteristics

The NM95HS0102HiSeC 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

applications

are

ideally

served

the

NM95HS0102 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 248 possible user combinations and en-

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 NM95HS0102 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 NM95HS0102 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

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

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

Figure 2 shows a general operational block diagram of the

NM95HS0102 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 CKOLED 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 CKOLED 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

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