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IF32
For a switching power pack:
DMX data < 76
DMX data > 180
DMX data between 76 and 180: do not use -
The DMX system is a high-speed digital data system, which
can transmit all the information required for light dimmers, multi-
motor lighting effects etc. down a single cable.
There is no limit to the number of units that can be connected
to the DMX signal, but it is not recommended that the total cable
length should exceed 250m.
Each unit connected to the DMX signal is given an address,
and it compares this to the data being sent on the DMX cable, so
it can determine which data is addressed to it. It then uses this
data to move a motor or set a brightness level as required by the
controller.
As the DMX system can transmit as much information as 512
analogue control wires down a single cable, it has to transmit
very quickly, in fact, at a frequency 12 times higher than the
highest audio frequency. Anyone who has used long leads for
audio will realise that it is difficult to do without losing the higher
frequencies. To make the DMX system work at such high
frequencies, it requires special circuitry and special cable.
Cable can be designed to pass high frequencies with no loss
if it has the correct resistance connected at each end, this
All NJD DMX products are designed to ensure that the
resistors are connected automatically. Without them, the signal
reflects off the end of the cable and interferes with the new data
coming the other way. If the cable is not correct, the system will
not work. Most good quality low-capacitance screened twisted
pair cables will work, but twin individually screened will not. Also,
© N.J.D. Electronics 1997
output definitely off
output definitely on
output may be on or off.
DM X.
resistance is called the characteristic
impedance of the cable. DMX cable has
a characteristic impedance of 120W.
User Guide
-Page 7-
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