Siemens SIMATIC NET PROFIBUS Owner's Manual page 387

6ZB5530–3AC30–0BA1
Converted to bit times this results in the following:
Transmission Rate
in Kbps
9.6
19.2
45.45
93.75
187.5
500.0
1500.0
Table 2: Delay Times of Fiber-Optic and RS 485 LAN Cables
To calculate the cable delay time, the maximum cable length in km is multiplied by the delay time
corresponding to the transmission rate from the table.
10.2.2 Delay Time of the PROFIBUS ILM
In contrast to the propagation time of electrical cables and fiber-optic cables, the delay time through the logic of
the PROFIBUS ILM clocked at the transmission frequency is not a physical time constant but depends on the
transmission rate. The number of logic levels in series is relevant with each causing a bit time delay.
The delay time per PROFIBUS ILM is 6 bit times from RS 485 input to infrared output when sending and 3 bit
times from infrared input to RS 485 output when receiving. The total delay time of the RS 485 input of the
sending PROFIBUS ILM to the RS 485 output of the receiving PROFIBUS ILM is therefore 9 bit times.
If several PROFIBUS ILM links are cascaded, the total delay time is the product of 9 bit times of the individual
links and the cascading depth.
10.2.3 Delay Time of Further Active PROFIBUS Network Components
Please refer to the delay time listed in the documentation of the specific product.
10.2.4 Transmission Delay Time TTD
The total delay time of the PROFIBUS network is the sum of all the values calculated in Sections 10.2.1 to
10.2.3.
Delay Time
in bit times per km
0.05
0.10
0.23
0.47
0.94
2.50
7.50
45
Infrared Link Modul (ILM)
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