Similar to CAN bus that communicates between ECMs in automotive applications, DALI provides two-way communications between lighting fixtures (“luminaires”), ballasts and controllers in buildings. It is defined in IEC technical standards IEC 62386 and IEC 60929, which cover LED drivers and electronic ballasts used in AC supplies with voltages up to 1000 V and with operating frequencies of 50 Hz or 60 Hz.
DALI uses Manchester-encoded 0 to 20 V signaling that enables a controller to address individual lights in a network or to broadcast commands to groups of lights in a zone.
Communication from the lights back to the controller is also possible, for reporting of parameters such as energy consumption and device failures.
DALI system cabling requirements are similar to conventional unidirectional 0 to 10 V controlled circuits deployed in commercial and industrial facilities. But with DALI the LED drivers and ballasts can be linked to a central computer, allowing each to be controlled independently.
LED drivers and ballasts are connected to make up a group of up to 64 LED drivers or ballasts. Each device is allocated an address, and the group is connected to a DALI controller. If more than 64 devices are needed for a particular building then groups can be linked together to create a “network of networks”. DALI does not require any hardwired power circuit control groups, but allows free-form network layout: daisy chain, star topology and multidrop are all permitted. A combination of two or more topologies is also allowed.
DALI has several advantages over conventional unidirectional lighting circuits:
DALI uses Manchester (biphase) encoding to send the Start bit and the information bits. The nominal data rate is 1200 bps, so one bit time is 833.33 µs. The embedded clock rate is double the data rate so has nominal timing of 416.67 µs, indicated as “Te”. The most significant bit (MSB) is transmitted first.
Forward frames are packets sent by the controller to the lighting / ballast device. They consist of one Start bit, eight address bits, eight data bits and two Stop bits. The bits are sent MSB first.
The first address bit defines 0 as a short address for individual devices or 1 for group or broadcast messages.
The last address bit is the Selector, which defines the following data byte with 0 as a direct arc power level or 1 as a command.
PicoScope can decode DALI waveforms: From the Tools menu select Serial Decoding then Create and select DALI from the list of available protocols.