UM1632 datasheet(4/32 Pages) STMICROELECTRONICS

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DALI information

UM1632

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DocID024513 Rev 1

The protocol used on these cables is a standard serial protocol.There is 1 start bit, 8 data

bits and 2 stop bits.The communication speed is fixed at 1200 Bd.Manchester coding is

used for improved resynchronization: rising edge is logical 1 and falling edge is logical 0.

Bytes are grouped into frames. One frame usually consists of 1 or 2 bytes, which is either

data only (answer from the device) or address + data (command to device).

Voltage levels present on DALI communication wires are higher than the transistor-

transistor logic (TTL) levels that are usually used. This is to provide better noise immunity to

higher interference from nearby power installation cables. Voltage levels are defined as

follows:

•

Low level state:

–

-4.5 to 4.5 V (transmitter)

–

-6.5 to 6.5 V (receiver)

•

High level state:

–

11.5 to 20.5 V (transmitter)

–

9.5 ... 22.5 V (receiver)

The low level state is dominant on the DALI bus. The device can force this level on the DALI

bus by shorting the DALI wires. Consequently, current levels are defined for devices used

on the DALI bus. There are two device types:

DALI master or DALI slave communication devices. In these devices, the current is

sunk from the DALI bus. They consume a maximum of 2 mA to receive high level state

and sink a minimum of 250 mA to transmit low level state.

DALI power supply. These devices power the DALI bus and are the source current for

it. Supply is limited to a maximum of 250 mA

The maximum length of the DALI bus depends on the cables used for the DALI

communication wires. The length is linearly dependent on the cross section of the

conductor. For example, a 1.5 mm2 cable (typically used in light installation cables) allows a

maximum bus length of up to 300 m.

Collisions between several DALI masters on the DALI bus are resolved on the basis of

timing priorities. When a collision is detected (the DALI master should check the sent data),

communication is muted for a period of time according to the assigned master priority. There

are five defined priority levels: 12 ms, 13 ms, 14 ms, 15 ms, and 16 ms. The longer the

waiting time, the lower the priority.

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