Gen VI Dimmer
User Manual
Page 40
8
DMX Explained
8.1
Overview
DMX512/1990-A is the industry standard for the transmission of digital control signals between
lighting equipment. It utilises just a single pair of wires on which is transmitted the level information
for the control of up to 512 DMX slots (addresses or channels). The information for each slot is
sent sequentially. The level of slot 1 is transmitted, then the level of slot 2, then 3, etc. up to a
maximum of 512 slots. This stream of data containing the levels for all 512 DMX slots is repeated
a minimum (Generally) of 44 times per second. This provides sufficient updates of channel
information for smooth fade transitions.
As the DMX512-A signal contains the level information for all slots, each piece of equipment
needs to be able to read the level(s) of the slots(s) that apply only to that piece of equipment. To
enable this, the GEN·
VI dimmer has a “DMX Patch” menu that allows you to patch (connect) each
DMX slot (address) from your lighting controller to a GEN·VI
channel number or to multiple
channel numbers.
When good quality data cables are used, DMX512 cable runs may be up to 1,000 metres in
length. When several DMX feeds are required (to feed different locations), DMX512 splitters must
be used. These provides multiple isolated DMX512 feeds. The GEN·VI
uses a high impedance
DMX input circuit allowing you to loop the DMX signal from one GEN·VI
to the next. The last
GEN·VI
in the chain must have the “DMX Terminate switch” set to TERM to terminate the line.
Note: Do not use unscreened microphone or low speed data cables for DMX. This can cause
problems in the DMX network. Make sure the cable conforms to the EIA485 cable requirements
by providing the following specifications:
•
Low capacitance
•
One or more twisted pairs
•
Foil and braid shielded
•
Impedance of 85 -150 Ohms, nominally 120 Ohms
•
22AWG gauge for continuous lengths over 300 metres
8.2
Typical DMX Installations
In the following example, the DMX output signal from the lighting control desk is fed to the DMX
connector of the first GEN·VI
dimmer. The DMX cable is then looped to the following GEN·VI
dimmers. The order of the daisy chaining is not important as each GEN·VI
channel can be
patched to any DMX slot number. The end of the DMX line is terminated to prevent the signal
reflecting back up the line and causing possible errors.
DMX
Cable
GenVI
DMX Slots
61-66
GenVI
DMX Slots
49-60
GenVI
DMX Slots
25-48
GenVI
DMX Slots
1-24
Lighting
Controller
Termination
Switch set to
TERM