NM95HS02EN datasheet(7/20 Pages) NSC

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Programmable Signal

Output Polarity

The transmit (TX) output pin signal polarity and quiescent

state output is controlled by the TxPol bit which may be

configured in EEPR0M If TxPol e 0 the TX output pin will

be at a logic low when no frame is transmitted or when a

‘‘0’’ appears as data in a frame Conversely if TxPoI e 1

the TX output pin will be at a logic high when no frame is

transmitted or when a ‘‘1’’ appears as data in a frame

This option allows the designer to choose between a config-

uration where a logic ‘‘1’’ represents power transmission

(for example when an RF stage is activated by driving the

base of an NPN transistor) and a configuration where a

logic ‘‘0’’ represents power transmission (for example when

an IR LED is connected between VCC and the TX output)

Data Frames

The NM95HS0102 HiSeC Generator transmits the encrypt-

ed data it generates as data frames These frames are

transmitted through an IR or RF transmitter stage using the

bit coding format selected

The NM95HS0102 transmits two types of data frames a

normal data frame and a synchronization (sync) frame The

format of each frame is similar but there are slight differenc-

es to suit the purposes of each Normal data frames are

used to transmit encoded data in general operation Sync

frames are used to synchronize (or initialize) the HiSeC to its

decoder

Data frames are comprised of a number of different fields

Each field occupies a fixed position in the data frame and

serves a specific purpose Most data fields are user-configu-

rable to some extent The user may enabledisable the

presence of a field control its length or modify its format

The user also has several options available to tailor the data

frame transmission format such as pause time between

frames and time-out time Options are configured by pro-

gramming the on-chip EEPR0M array The content and for-

mat of each of the fields is discussed below

NORMAL DATA FRAME

The NM95HS0102 HiSeC Generator transmits normal data

frames in general operating mode Frame transmission be-

gins each time a key switch is asserted and continues as

long as the key is held down The device has an option to

terminate transmitting data frames and go into halt mode if

a key is held down for more than 80 seconds (if the

TlMEOUTEN feature has been enabled)

The normal data frame format contains both dynamic code

and key application data (in the data field) Since the length

of several fields is adjustable there are several possibilities

for the length of the data frame The shortest possible nor-

mal data frame is 29 bits and the longest possible normal

data frame is 92 bits 24 bits of dynamic code 4 bits of key

application data and 1 stop bit are always present

The composition of a normal data frame is shown in

Figure 4

SYNC FRAME

The NM95HS0102 HiSeC Generator transmits sync

frames only in sync mode so that it can synchronize itself

with its decoder This mode occurs only during initialization

of the device or after holding a key down for more than 10

seconds (if the AutoResync feature has been enabled)

The sync frame format contains both start code and a fixed

4-bit sync code of 0000 This sync code replaces the key

application data in the data field and is used to confirm

HiSeC sync mode to the decoder

Sync mode is built into the generator to allow resynchroni-

zation of the device under certain conditions as a conve-

nience to the end user If the designer wishes to preclude

any possible resynchronization the presence of the sync

code allows the decoder to detect any synchronization at-

tempt

Since the length of several fields is adjustable there are

several possibilities for the length of a sync frame The

shortest possible sync frame is 45 bits and the longest pos-

sible sync frame is 96 bits 40 bits of start code 4 bits of

sync code and 1 stop bit are always present

The composition of a sync frame is shown in

Figure 5

011 bits

08 bits

02024 bits

4 bits

2436 bits

08 bits

1 bit

Preamble

Sync

Key ID

Data

Dynamic

Parity

Stop

Field

Code

Field

Bit

FIGURE 4 Normal Data Frame Configuration

011 bits

08 bits

02024 bits

4 bits

40 bits

08 bits

1 bit

Preamble

Sync

Key ID

Sync

Start

Parity

Stop

Field

Code

Field

Bit

FIGURE 5 Sync Frame Configuration

Data Frame Fields

Data frames are comprised of a number of data fields Each

field occupies a fixed position in the data frame and serves

a specific purpose Most data fields are user-configurable by

programming the on-chip EEPROM array The content and

format of each field is discussed below as well as the EEP-

ROM options available

All data frame fields are transmitted Most Significant Bit

first

THE PREAMBLE

The user has the option of allowing a preamble to be trans-

mitted as the first frame of either a normal data frame or a

sync frame This option is enableddisabled by setting the

PreamblePresent bit in the EEPROM array PreamblePre-

sent e 0 means no preamble is transmitted PreamblePre-

sent e 1 means an 11-bit preamble is transmitted as de-

scribed below

The purpose of the preamble is to generate a relatively long

clearly recognizable bit pattern to give the decoder a

chance to ‘‘wake up’’ and configure its logic circuits and

registers This allows the receiver to be placed in a standby

mode to conserve power for battery applications

The preamble is only transmitted once as the first frame of a

data transmission regardless of how long the key is held

down although the remaining frames of the data transmis-

sion (including any inter-frame pauses) will continue to re-

peat as long as the key remains depressed

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