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8
Overview
Many products and applications call for the transfer of button presses
or switch closures across a wireless link. Traditionally, a remote control
link has operated in only one direction, from a transmitter to a receiver.
The cost associated with transceivers has been too high to practically
implement in low-cost products. With the increasing availability of low-cost
transceiver solutions, bidirectional links are now practical and open a new
world of opportunity.
In a wireless environment, maintaining the reliability and uniqueness of a
transmitted signal is generally of great importance. In a unidirectional
system, IC devices called encoders and decoders are often utilized to
simplify this process. The encoder side turns the status of a number
of input lines into an 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 decoder’s output lines are set to replicate the status of
the encoder’s input lines.
To accommodate bidirectional links, a new type of device has been
developed. Called a transcoder, this device combines a remote control
encoder and decoder into a single device, and is capable of sending
commands as well as receiving them. It is also able to receive an automatic
confirmation from the remote side indicating that its command was
received and the appropriate action was taken. For example, verifying that
an automobile’s doors are all closed and have locked, or a remote valve
has actually closed.
The Linx MT Series is a revolutionary transcoder product designed for
wireless remote control applications. The same device can be used as an
encoder, decoder, or transcoder and is ideal for both uni and bidirectional
applications and even mixtures of the two. The MT Series is easily
implemented, making it ideal for even the most basic applications, but
its rich feature set also allows it to meet the needs of far more complex
applications. These features include the ability to identify the originating
transmitter, establish user permissions, select output latch modes on a
“per pin” basis, and a powerful serial interface that allows control and
information exchange with external microcontrollers or a PC.
Consider a brief example of how just one of the MT’s innovative features
could be used to transform a relatively simple application, the common
garage door opener. In competitive devices, encoded transmissions