Cycle times PLC tasks
For practical application, the cycle times of the PLC tasks should, if possible, always be set so that the maximum data transfer rate from the DALI bus is achieved.
Tests were performed to determine the number of frames at different cycle times of the PLC tasks. For this purpose, a PLC program was used, which cyclically sends 6 frames independently of each other. Three 16-bit frames (2 x without backward frame, 1 x with backward frame) and three 24-bit frames (2 x without backward frame, 1 x with backward frame) were sent. Since the send-twice frames are only of importance for the configuration of DALI devices, they were not considered further. The total transmission length of the 6 frames was thus 238 ms (2 x 21.2 ms + 46.7 ms + 2 x 37.8 ms + 53.3 ms). This means that the sample program could send a maximum of 25 frames per second (1000 ms / 238 ms x 6). Events that are additionally sent by possible DALI sensors (input devices) are not taken into account.
| 80 ms | 60 ms | 40 ms | 30 ms | 20 ms | 10 ms | 8 ms | 6 ms | 4 ms |
|---|---|---|---|---|---|---|---|---|---|
30 ms | 6 | 7 | 7 | 8 | 8 | 8 | 8 | 8 | 8 |
15 ms | 11 | 11 | 12 | 12 | 13 | 13 | 13 | 13 | 13 |
10 ms | 15 | 15 | 16 | 17 | 17 | 17 | 17 | 17 | 17 |
8 ms | 18 | 18 | 19 | 19 | 20 | 20 | 20 | 20 | 20 |
6 ms | 20 | 21 | 21 | 22 | 22 | 22 | 22 | 22 | 22 |
4 ms | 23 | 23 | 24 | 25 | 25 | 25 | 25 | 25 | 25 |
2 ms | 23 | 24 | 25 | 25 | 25 | 25 | 25 | 25 | 25 |
The times in the top line (4 ms ... 80 ms) specify the cycle time of the PLC task from which the DALI commands are started. The times (2 ms ... 30 ms) in the first column specify the cycle time of the PLC task for background communication.