Posted on: July 1, 2014
DALI networks have a controller and one or more lighting devices that communicate through DALI interfaces. The controller can monitor and control each luminaire using bi-directional data exchange. The DALI protocol allows devices to be individually addressed or using group and scene broadcast messages to simultaneously address multiple devices
Each luminaire is assigned a unique static address in the numeric range 0 to 63, making possible up to configure 64 devices in a single system. To address more than 64 devices DALI can be used as a subsystem via gateways. Data is transferred between controller and devices by means of an asynchronous, half-duplex, serial protocol over a two-wire differential bus, with a fixed data transfer rate of 1200bits per second.
DALI controllers only require a single pair of wires for communication to all the devices on a single DALI network. The network can be arranged in a bus or star configuration or a combination of these. The DALI System is not classified as being SELV and therefore may be run next to the mains cables or within a multi-core cable that includes mains power. The DALI data is transmitted using a system called Manchester encoding that has a high signal to noise ratio which enables reliable communications in systems with high electrical interference. DALI systems are not polarity specific due to the integral diode bridge technology.
DALI signal levels are defined as 0±4.5 V for “0” and 16±6.5 V for “1” with the central interface current maximum of 250 mA and unit power maximum of 2 mA. The cabling should be a minimum 600V mains rated, 1mm cross section and a maximum volta drop of 2V/300M. The signal interface is isolated and does not require termination resistors
Originally the configuration data was stored in EEPROMs which had limited write cycles. These have been replaced by RAM where frequent configuration changes are required, significantly reducing the requirements for EEPROM rewriting.