Pathway DMX Pathfinder CR Manual - Manual (Page 9)

DMX Distribution System Page 9
Operation
systems since the early 1980s. Included are Avab A-240, Colortran CMX
(also called D192 and C-156), Electro Controls EC-Mux, and Kliegl K96 and
K100. All of these are compatible with the DMX Distribution System, since
they are designed to work with RS-422A or RS-485 systems. In addition,
manufacturers of automated lights have developed their own control
protocols (sometimes called native protocols) that are for the most part
compatible with the system. Incompatible protocols would include analog-
based or synchronous systems such as ETC/LMI protocol, NSI Microplex,
and Strand AMX-192 and D54.
In 1985, a standardized asynchronous protocol was established for adoption
by the entire lighting control industry. USITT DMX512 is now the most
commonly used lighting control communications protocol in the world.
.9 Transparency -- Transparency has one accepted definition in data
communications, and an additional meaning with respect to the DMX
Distribution System. The first relates to the ability of a communications
protocol to pass messages with random bit patterns, even when those
patterns may unintentionally duplicate the bit patterns of control codes. In the
case of the DMX Distribution System, we would be mostly correct in referring
to it as a transparent data communications network since any digital protocol
that meets the basic requirements of E.I.A. RS422A/485 will work with the
system.
As described in Section 1.1, the DMX Distribution System is essentially a facility for
carrying DMX data communications from the source(s) to where it is needed for
remote control of various elements of the lighting system. Several technical
problems must be overcome for such a scheme to function properly, safely and
reliably, and to avoid breaking the basic rules set out in the E.I.A. RS422A/485
specifications. These are:
.10 Topology -- This is the physical arrangement of the data communications
system. The topology of the DMX Distribution System will at first appear to
be a many-pointed star, since wiring emanates in individual runs to each
source location and receiving station from the distribution rack. Correct
wiring practice for RS422A/485 necessitates a point-to-point or multi-drop