Serial Communications; Ir (Infrared) - Crestron SIMPL Windows User Manual

Software
Crestron IR wireless interface
8 • Crestron SIMPL Windows
direct control of motors and lighting circuits. In addition, relays can either be
mechanical or solid-state. If you are unsure about what type of relay is needed for a
given application, you can call Crestron technical support for assistance.

Serial Communications

Many devices today can be controlled using various types of serial communication.
Typically serial-controlled devices use one of the following types of serial
communication: Infrared, RS-232, RS-422, RS-485, MIDI, and "custom serial". In
the next few paragraphs we will discuss the differences between these formats.
What does "serial" mean?
The term serial describes a communications format in which one piece of
information is transmitted and/or received after the next. As an analogy, think of a
telephone where you hear one word after word until a sentence is constructed. This is
different from parallel communications in which multiple pieces of information are
transmitted and received simultaneously.
Serial communication encompasses a wide variety of popular formats, many of
which are supported directly with Crestron control systems. The sections below
describe the most common formats in more detail.

IR (Infrared)

For many years infrared remote control has been very popular, and today it remains
among the most common forms of serial control. As the name implies, infrared
control consists of serial data transmitted via pulses of infrared light. In addition, IR
signals are usually modulated by a carrier signal. In most cases this carrier signal has
a frequency of approximately 40kHz, though some can go as high as 1MHz.
In the Crestron world there are two applications of IR control. Crestron wireless user
interfaces may use IR for communication with the control system. In this case the IR
is transmitted/received by Crestron equipment is in a proprietary format.
The other application of IR control is IR signals that the system generates to control
other manufacturer's devices (e.g. to mimic Sony or Panasonic). The system can
generate the functions that were available on the device's remote control.
Since IR is a one-way communication, there is no feedback from the equipment
being controlled. That is, data is transmitted to the device to be controlled, but no
data is returned from the device to the control system. This means that when using
IR control, you have no true feedback from the device telling you that your
command was accepted, for example. This is one inherent disadvantage with this
type of control. Another disadvantage of IR is that it depends upon a line-of-sight
between the control system and the device to be controlled. To counter this problem,
Crestron can provide an IR probe, which provides a wired connection from the
Crestron SIMPL Windows
Primer – DOC. 6253