LICAL-ENC-MS001(2008) Просмотр технического описания (PDF) - Unspecified
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LICAL-ENC-MS001 Datasheet PDF : 7 Pages
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DESIGN CONSIDERATIONS
The Linx MS Series encoders and decoders are designed for remote control
applications. They provide an easy way to securely register button presses or
switch closures over a wireless link. The encoder side turns the status of eight
parallel input lines into a secure, encoded, serial bit-stream output intended for
transmission via an RF or infrared link. Once received, the decoder decodes,
error checks, and analyzes the transmission. If the transmission is authenticated,
the output lines are set to replicate the status of the lines on the encoder.
Prior to the arrival of the Linx MS Series, encoders and decoders typically fell into
one of two categories. First were older generation, low-security devices that
transmitted a fixed address code, usually set manually with a DIP switch. These
address lines frequently caused the user confusion when trying to match a
transmitter to a receiver. Another disadvantage was the possibility that address
information could be captured and later used to compromise the system.
These concerns resulted in the development of a second type of encoder /
decoder that focused on security and utilized encryption to guard against code
cracking or code grabbing. Typically, the encoding of each transmission changes
based on complex mathematical algorithms to prevent someone from replicating
a transmission. These devices gained rapid popularity due to their high security
and the elimination of manual switches; however, they imposed some limitations
of their own. Such devices typically offer a limited number of inputs, the
transmitter and receiver can become desynchronized, and creating relationships
and associations between groups of transmitters and receivers is difficult.
The Linx product line, which includes the MS and HS Series, is the first product
line to offer the best of all worlds. Both series accept up to eight inputs, allowing
a large number of buttons or contacts to be connected. The devices also allow
relationships among multiple encoders and decoders to be easily created.
Security is well provided for. The MS Series uses a random fixed word with 224
possible combinations to give a high level of uniqueness and a reasonable level
of security. For applications requiring the highest security, the HS Series, which
employs tri-level, maximum-security encryption, should be considered.
Encoder transmission protocol and methodology is a critical but often overlooked
factor in range and noise immunity. The MS and HS products utilize a true serial
data stream rather than the PWM schemes employed by many competitive
devices. This allows products based on MS or HS devices to achieve superior
range and immunity from interference, edge jitter, and other adverse external
influences.
One of the most important features unique to the MS and HS products is their
ability to establish a unique user identity and profile for the device containing the
encoder. In conventional designs, all encoded transmissions are either
recognized or denied based on the address. In cases where encoder and
decoder addresses match, the state of all data lines is recognized and output.
Linx products uniquely allow a user or manufacturer to define which encoder
inputs will be acknowledged by each decoder. MS series decoders can store up
to 40 system users and unique profiles for each. This allows for an incredible
variety of unique relationships among multiple system components and opens
the door to product features not previously possible.
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A PRACTICAL EXAMPLE
Consider this practical example: a three door garage houses Dad’s Corvette,
Mom’s Mercedes, and Son’s Yugo. With most competitive products, any user’s
keyfob could open any garage door as long as the addresses match. In a Linx
MS-based system, the keyfobs could easily be configured to open only certain
doors (guess which one Son gets to open!) The MS Series also allows for
component grouping. Imagine a remote control designed for use in a woodshop.
One button could turn on a vacuum, one an air cleaner, and another a light, yet
another button could then be user configured to turn on all of them with a single
touch. As you can see, the MS Series uniquely combines security and simplicity
with the power to create groups and relationships.
Manual Address Encoders
Advantages ☺
High number of button inputs
Disadvantages
Low-security fixed code
Confusing manual addressing
Low number of addresses
PWM data output
High security vulnerabilities
“Rolling Code” Encoders
Advantages ☺
Highly secure
Eliminates manual address settings
Disadvantages
Low number of button inputs
Encoder and decoder can become unsynchronized
Difficult or impossible to create relationships
Security vulnerabilities
Linx Encoders
Advantages ☺
High number of button inputs
Highly unique (MS)
Highest security available on the market (HS)
Eliminates manual address settings
Allows for associative relationships
Cannot unsynchronize
Serial data output
Encoder ID is output by the decoder
Latched or momentary outputs (MS)
External transmitter and receiver control lines
Disadvantages
Slightly higher cost for some basic applications
Security vulnerabilities (MS only)
Figure 5: Encoder Comparison Table
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