DALI (Digital Addressable Lighting Interface) is a data protocol and transport mechanism that was jointly developed and specified by several manufacturers of lighting equipment. The common platform of DALI enables equipment from different manufacturers to be connected together.
DALI network consists of a controller and one or more lighting devices (e.g., electrical ballasts and dimmers) that have DALI interfaces. The controller can monitor and control each light by means of a bi-directional data exchange. The DALI protocol permits devices to be individually addressed and it also incorporates Group and Scene broadcast messages to simultaneously address multiple devices (e.g., "Group 1 goto 100%" or "Recall Scene 1").
Each lighting device is assigned a unique static address in the numeric range 0 to 63, making possible up to 64 devices in a standalone system. Alternatively, DALI can be used as a subsystem via DALI gateways to address more than 64 devices. Data is transferred between controller and devices by means of an asynchronous, half-duplex, serial protocol over a two-wire bus, with a fixed data transfer rate of 1200 bit/s.
DALI requires a single pair of wires to form the bus for communication to all devices on a single DALI network. The network can be arranged in a bus or star topology, or a combination of these. The DALI System is not classified as SELV (Separated Extra Low Voltage) 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 manchester encoding and has a high signal to noise ratio which enables reliable communications in the presence of a large amount of electrical noise. DALI employs a diode bridge in the interface circuitry so that devices can be wired without regard for polarity. Signal level are defined as 0±4.5 V for "0" and 16±6.5 V for "1". Central interface power maximum is 250 mA and 2 mA per unit. The network cable is required to be mains-rated, with 600 V isolation and at least a 1 mm cross-section, with a maximum drop of 2 volts along the cable (max 300 m). Signal interface is galvanically separated and doesn't need any termination resistors. DALI is a step on from the DSI protocol, which is used by HF fluorescent ballasts. One of the main advantages that DALI has over earlier systems is that each device on a segment of data cable can be separately addressed, as DSI and 1-10V devices are not separately addressable and can only be controlled as a group. The net result is that to achieve similar control functionally, DALI requires less complex (and therefore less expensive) wiring topology than DSI or 1-10V devices.
