nm95hs02 National Semiconductor Corporation, nm95hs02 Datasheet - Page 7

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

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
be at a logic low when no frame is transmitted or when a
‘‘0’’ appears as data in a frame Conversely if TxPoI
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 V
Data Frames
The NM95HS01 02 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 NM95HS01 02 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 enable disable 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 NM95HS01 02 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 NM95HS01 02 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)
e
0 the TX output pin will
CC
and the TX output)
e
1
7
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
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 enabled disabled by setting the
PreamblePresent bit in the EEPROM array PreamblePre-
sent
sent
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
Preamble
Preamble
0 11 bits
0 11 bits
e
e
FIGURE 4 Normal Data Frame Configuration
0 means no preamble is transmitted PreamblePre-
1 means an 11-bit preamble is transmitted as de-
0 8 bits
0 8 bits
FIGURE 5 Sync Frame Configuration
Sync
Field
Sync
Field
0 20 24 bits
0 20 24 bits
Key ID
Key ID
Field
Field
Code
4 bits
Data
Field
4 bits
Sync
24 36 bits
Dynamic
40 bits
Code
Code
Start
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0 8 bits
0 8 bits
Parity
Parity
Field
Field
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Stop
Stop
1 bit
1 bit
Bit
Bit