Channel Characteristics; Parts Of An Output Channel; The Device-Channel Concept; Defining Latching - AMX AXCESS CONTROL SYSTEM PROGRAM Instruction Manual

Channel Characteristics

Channel Characteristics
This section contains information on channel characteristics and how to change the way the status
of an output channel behaves. It includes explanations of channel concepts, and examples of
Axcess programming code. In this chapter, you will learn how to change the status behavior, which
in turn changes the way a channel reacts when it is activated by the output change keywords.

Parts of an Output Channel

An output channel actually has two parts: the physical part and the status part, as shown in FIG. 4.
FIG. 4 Parts of an output channel.
The physical part is the physical device-dependent control, such as a relay on a relay card, a button
light (lamp) on a Touch Panel, or an infrared pattern in an infrared card. The status reports the state
of the physical part. Typically, these two parts act exactly the same; when one is on, so is the other.

The Device-Channel Concept

Everything that an Axcess Control System controls is controlled through a device in the system.
Each device communicates to the Central Controller through AXlink, the Axcess Control System's
communication bus. Most devices, such as a Touch Panel or a relay card, have channels which
either generate an input, accept an output, or both. These inputs and outputs are referred to in the
Axcess program as a device-channel, which is written like this:
TO[DEVICE,Channel]
This the device-channel is the most fundamental concept of the Axcess Control System, as it is the
most common way that Axcess communicates to the outside world.

Defining Latching

The default status of all channels is momentary. When a momentary channel is activated with a TO
keyword, it activates its output and status only as long as the button which activated the TO
keyword is pressed. For example, the Focus channel for slide projectors is momentary. When the
corresponding Focus button is pressed, the slide projector will focus. The projector will continue to
do so until the button is released.
However, some devices need their particular channel to stay ON to operate. If so, the channel can
be made latching by being placed in the DEFINE_LATCHING section. Once a latching channel is
activated by a TO keyword, the channel changes its state from OFF to ON (assuming it was
previously off). However, when the TO keyword stops activating the channel (its corresponding
Axcess Programming Language 19