–

–

–

–

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

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.