ST STM32F1 Series User Manual page 5

UM1728
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 better 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 due to better noise immunity
because of higher interference present on nearby power installation cables. Voltage levels
are defined as follows:
•
Low level state
–
–
•
High level state
–
–
Low level state is dominant on the DALI bus. The device can force this level to the DALI bus
by shortening the DALI wires. Consequently, current levels are defined for devices used on
the DALI bus. There are two device types:
1. 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.
2. 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 (for example, a 1.5 mm2 cable (which is typically used in light
installation cables) allows a maximum bus length of up to 300 m.). The length is linearly
dependent on the cross section of the conductor.
Collisions between several DALI masters on the DALI bus are solved 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 longest waiting
time has less priority.
-4.5 to 4.5 V (transmitter)
-6.5 to 6.5 V (receiver)
11.5 to 20.5 V (transmitter)
9.5 to 22.5 V (receiver)
DocID025866 Rev 1
DALI information
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