Doug Fleenor Design 1211 - Manual (Page 3)

OPERATION
The DMX512 splitter has no operator controls; it is fully automatic. It should be left plugged in at
all times for automatic operation. When a DMX signal is applied to the input, it is processed by the
receive circuit, isolated by the optical couplers, and retransmitted by the driver circuits. All this
takes less than 1/10,000,000 of a second.
When no DMX input is present, the outputs are placed in an idle condition. This condition is
defined in the DMX512 specification as Data+ line high and Data- line low.
Two indicators are provided on the front panel of the splitter. The red POWER indicator is
illuminated whenever the power cord is plugged into a live outlet. The green SIGNAL indicator is
illuminated whenever the Data+ and Data- lines leave their idle state. Note that the signal indicator
does not necessarily indicate a valid signal, only that the line is not idle.
The signal indicator will change intensities as the levels sent to the outputs are varied. In some cases
the signal indicator may be quite dim even though data is being received. The indicator will be at
its lowest intensity when all dimmers are being sent to full. Try sending all dimmers to zero then
look at the indicator.
LINE TERMINATION
The input of the one, three, and five output models are terminated with 120 ohm 1/2 watt resistors.
This is the proper input termination for DMX512 lines. Since these models do not provide pass-
through of the input DMX signal, the unit is always the last device on the line. (These unit may be
customized with a feed through, in which case it must be terminated.)
The input of the eleven output model is not terminated. To properly terminate the DMX input, a 120
ohm termination plug must be plugged into on the pass-through connector.
It is recommended that all control runs be terminated. The most important place to use termination
is on a control run where the signal daisy chains from a source (console, isolator, splitter, etc.) to
several receivers (dimmers, color scrollers, etc.) with hundreds of feet separating the receivers. What
happens in such a case is that the signal seen by the receivers is a combination of the correct signal
(sent by the console) and a delayed version of that signal which is reflected from the end of the cable.
The longer the cable, and the more devices on the cable, the more the reflected signal tends to distort
the initial signal. The cure (in theory) is to absorb the signal at the end of the cable so that none is
reflected back up the line.
To terminate a typical control run place a 120 Ohm resistor between the Data+ (pin
3) and Data- (pin 2) lines at the last receiver on the line.
Unused outputs on a DMX512 splitter do not need to be terminated.