DALI  Digital Signal
 

DALI protocol is a half-duplex digital communication composed of forward and backward frames, and it uses the bi-phase Manchester asynchronous serial data format.  The convention of Manchester coding specified by IEEE is that a logic '0' is represented by a High-Low signal sequence, and a logic '1' is represented by a Low-High signal sequence. The data transition rate is 1200 bit/sec, and thus the bit period is 833 micro second.

A DALI transmission consists of 2 types of message frames, namely, forward frame (sent by a controller) and backward frame (answered by a luminaire/device). The backward frame will only be answered, if the forward frame includes a command which queries the luminaire/device. The response time of luminaire/device to a query commanded by a forward frame is between 2.92 milliseconds and 9.71 milliseconds.

 
 

Forward Frame

 
  A forward frame consists of 19 bi-phase encoded bits: 1 start bit, 1 address byte and 1 data byte. The frame is terminated by 2 stop bits. The stop bits do not contain any change of phase.
  • 1 start bit (logical ??
  • 1 address byte (8-bit address)
  • 1 data byte (8-bit data)
  • 2 high level stop bits (idle)
 
  Backward Frame

A backward frame consists of 11 bi-phase encoded bits: 1 start bit and 1 data byte. The frame is terminated by 2 stop bits. The stop bits do not contain any change of phase.
  • 1 start bit (logical ??
  • 1 data byte (8-bit data)
  • 2 high level stop bits (idle)
 
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