On any PROFIBUS, certain time ratios must be respected to ensure that a telegram sequence can function correctly.
After a synchronization pause lasting TSYN to mark the beginning of a sequence, the Request telegram is sent by the master to the slave. The slave should start its response no sooner than min TSDR (SDR = Station Delay of Responder), but no later than max TSDR. The min TSDR time must include at least the TQUI time of the in-line amplifier and repeater and the TRDY time of the master. In modern PROFIBUS-DP systems, min TSDR = 11. Slower PROFIBUS-FMS slaves have min TSDR values of up to 255 tBit. The master waits for a response from a slave for a maximum period of TSL (SL = slot). This time is determined by max TSDR.
Time ratios
All times listed here can be read and adjusted as FDL parameters.
Parameter |
Bit rate in kBit/s |
|||||
≤ 187.5 |
500 |
1500 |
3000 |
6000 |
12 000 |
|
TQUI |
0 |
0 |
0 |
3 |
6 |
9 |
TSET |
1 |
1 |
1 |
4 |
8 |
16 |
TRDY |
≤ 11 |
≤ 11 |
≤ 11 |
≤ 11 |
≤ 11 |
≤ 11 |
min TSDR |
11 |
11 |
11 |
11 |
11 |
11 |
max TSDR |
60 |
100 |
150 |
250 |
450 |
800 |
TSL |
100 |
200 |
300 |
400 |
600 |
1'000 |
Table of default values for times