Structure data frame
Each Forward Frame (FF) and Backward Frame (BF) basically consists of:
- 1 start bit
- n data bits
- 1 stop condition
The most significant bit (MSB) is transmitted at the beginning.
Transmission is via Manchester coding with a data transfer rate of 1200 bits per second. Thus, each bit has a length of 0.833 ms (1 / 1200 = 0.000833).
The Stop condition has a length of at least 2.45 ms.
A fixed time (settling time) must be waited between the sending of two data frames before the sending of the next data frame can be started.
The length of the settling time depends on the DALI priority with which a data frame is sent. The higher the DALI priority, the smaller the settling time.
Settling time | Minimum | Mean value | Maximum |
|---|---|---|---|
between FF and BF | 5.5 ms | 8.0 ms | 10.5 ms |
before each FF (DALI priority High) | 13.5 ms | 14.1 ms | 14.7 ms |
before each FF (DALI priority Middle high) | 14.9 ms | 15.5 ms | 16.1 ms |
before each FF (DALI priority Middle) | 16.3 ms | 17.0 ms | 17.7 ms |
before each FF (DALI priority Middle low) | 17.9 ms | 18.6 ms | 19.3 ms |
before each FF (DALI priority Low) | 19.5 ms | 20.3 ms | 21.2 ms |
More information about DALI priorities is also available in the chapter Priorities.
Thus, data frames with a higher DALI priority (low settling time) occupy the DALI bus earlier, compared to data frames with a lower DALI priority (high settling time).
Certain DALI commands must be sent twice within 100 ms (send-twice) without the receiver being allowed to receive another DALI command in the meantime. Only then will the DALI command be recognized as valid by the receiver. This is primarily used with DALI commands that are used to configure DALI devices. So that the two DALI commands are not interrupted by another DALI command, the 2nd DALI command is always sent with DALI priority High. The DALI priority High is reserved for these DALI commands and must not be used in any other context.