TRC1300 Datasheet, PDF (9/27 Pages) Texas Instruments – MARCSTAR I E/D REMOTE CONTROL ENCODER/DECODERS

TRC1300, TRC1315
MARCSTAR™ I E/D
REMOTE CONTROL ENCODER/DECODERS
SLWS011D – AUGUST 1996 – REVISED JANUARY 1997
PRINCIPLES OF OPERATION
general (continued)
Each of the TRC1300 and TRC1315 MARCSTAR I E/D devices can be pin-selected for operation as either an
encoder on the transmitter end of a remote control system, or as a decoder on the receiver end. The intervening
medium can be a wired, RF, IR, or any other type of link with sufficient bandwidth to pass the signal. The objective
is to transmit a function code to the remote receiver to initiate an event or for some other purpose, with the
highest level of certainty that the function code is only accepted from the matching encoder and not from any
other.
A MARCSTAR I E/D device operating in the encoder mode can send four different function codes either
individually or in any combination to activate up to 15 different functions at the decoder.
Once a decoder learns a security code from an encoder, it then responds only to that particular encoder. A
MARCSTAR I E/D device operating in the decoder mode can learn and respond to as many as four different
encoders and provides four independent function outputs. These outputs can be further decoded (externally)
to provide a 1-of-15 function output.
hopping code
The MARCSTAR I E/D devices use an advanced hopping-code algorithm to significantly increase the security
level of the system. The security code sent by the encoder and the security code accepted as valid by the
decoder change after each transmission. This is done independently for each of the four separate encoder
security codes learned by the decoder.
As an encoder, the MARCSTAR I E/D is shipped from the factory with a unique 40-bit security code stored in
on-board nonvolatile memory (EEPROM). Since every device shipped has a unique code, it is ready for
immediate use and requires no reprogramming. Then, each time a function input is activated, the encoder
fetches the 40-bit security code from EEPROM and encrypts it. Next, the encoder assembles the data frame
to be output, and then sends it out. The data frame consists of the synchronizing bits, the encrypted security
bits, the function data bits, a dummy bit, and the blank-time bits. After the data frames output ends, the encoder
immediately increments the 40-bit security code by applying the special hopping-code algorithm to it and then
stores the results in EEPROM for the next time a function input is activated. Thus, each time a function input
is activated, the 40-bit security code that is sent out is different from the security code in the previous
transmission. And with more than a trillion possible combinations, the same code is never sent twice over the
lifetime of a system.
As a decoder, the MARCSTAR I E/D initially learns the 40-bit security code stored in a particular encoder by
receiving it and storing it in on-board EEPROM. Each time a security code is received from an encoder, the
device decrypts the received 40-bit security code and compares it with the next security code expected from
any of the learned encoders. The next expected security code is calculated by applying the same hopping-code
algorithm used in the encoder to the 40-bit code stored in the decoder memory. If the received security code
matches the next security code expected from one of the learned encoders, it is declared valid and the attached
function code is decoded. If the function code is valid, the appropriate function output or outputs are asserted.
The just-received 40-bit security code is then incremented according to the algorithm, becoming the next
security code expected from that encoder, and stored in EEPROM for next time. If the received security code
does not match the next expected code from one of the learned encoders, the received function data and
security code are ignored.
Because the decoder activates function outputs only when the next expected code in the hopping-code
sequence is received, interception and subsequent retransmission of the same code does not activate the
decoder function outputs.
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