Linx Technologies LICAL-ENC-MS001 - Manual (Page 6)

– – – – 6 7
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 2
24 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 are 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.
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.
The MS Series uniquely combines security and simplicity with the power
to create groups and relationships. Figure 8 compares the advantages and
disadvantages of different encoders.