DIN Rail 2 Channel DALI Interface
Crestron
DIN-DALI-2
2
•
DIN Rail 2 Channel DALI Interface: DIN-DALI-2
Programming Guide – DOC. 7365A
Operation of the DIN-DALI-2
The DIN-DALI-2 consists of a DALI power supply, an Ethernet/Cresnet
®
controller,
and two independent DALI drivers that are isolated from earth ground and from
Ethernet/Cresnet. The following paragraphs provide detailed information on the
power supplies, wiring, and ballast communication to assist with troubleshooting the
device.
Power Supplies
The DALI loops are not isolated from each other. Loop 1 and Loop 2 share the same
common circuit.
The built-in DALI power supply provides 15 V (~14.8 V) on the DALI lines. Meter
measurement shows less since data transmission reduces the average voltage.
The DALI supply uses a current limit set at 250 mA. Drawing more than 250 mA
causes the output to collapse. Each loop has its own 250 mA limit. During normal
operation, DALI ballasts draw ~1 mA each from the loop (2 mA max).
The DALI unit, including DALI bus power supply, can be powered from Cresnet
24 V or from PoE. If both are connected, power is drawn from Cresnet. If both are
connected and Cresnet power is removed, the unit resets.
An external slide switch can be used to disable the internal power supply should an
external supply be used. This is not recommended and there is no known reason to
do this other than for troubleshooting. Sliding the switch to
EXT
removes power
from the loops and causes all ballasts to go to their emergency levels (full).
Communication with Ballasts
In order to communicate, devices short circuit the DALI loop. This causes 250 mA
to be drawn from power supply and voltage to collapse. Devices register the voltage
on the loop to represent a high or low bit. The DALI specification dictates that a
logic low is when the bus voltage is less than 6.5 V while a logic high is greater than
9.5 V. Values in between are not defined. The DIN-DALI-2 uses a threshold of
~7.5 V to determine a low or high state.
Communication between DIN-DALI-2 and ballasts is two-way. Ballasts only talk
when queried—when a command is sent to the ballast requesting its level or status.
The DIN-DALI-2 translates the digitals and analogs received from the control
system in DALI packets. Since the communication speed on the DALI network is so
slow, the DIN-DALI-2 reports a simulated (estimated) position whenever a
command is received from the control system. The actual level is requested from the
ballasts afterward so an accurate position can be reported to the control system.
The DIN-DALI-2 also polls all ballasts on the loop, regularly requesting their current
level and status. The status of the ballast is also queried at a slower pace. This tells
the DIN-DALI-2 if a lamp is out or if a ballast has just powered up. It also updates
the DIN-DALI-2 internal list of connected ballasts. If a ballast is deemed not
connected, it is polled at a much slower rate.
DALI ballasts do not recall their last level on power up. Instead they go to the
Power-On Level
setting, typically 100%. The DIN-DALI-2 recognizes a ballast has
just powered up based on its query status response and sends the correct level to
which that ballast should go.
