PROFINET/Ethernet
5.3 Timing and runtimes
Power Line Booster
Operating Instructions, 11/2019, A5E36203125A-AG
75
Figure 5-3
Maximum latency time for bidirectional communication
Bidirectional communication here means that the IO controller sends a query and the IO
device responds using the same communication path, e.g. by sending an acknowledgment.
Bidirectional communication results in the chart as seen in the figure above. We assume
here that the PN update time T
PN
is significantly shorter than the latency time caused by the
PLB system T
PLB
.
The result is the time below:
T
Lat
= 2 • T
Ctr
+ T
PN
+ 2 • T
PLB
When you replace these with typical
values (T
Ctr
= 30 ms, T
PN
= 128 ms, T
PLB
= 400 ms, T
Dev
= 10 ms), you get:
T
Lat
= 2 • 30 ms + 128 ms + 2 • 400 ms = 988 ms.
The following graphic serves as a starting point for determining the PROFINET times. The
gray graph shows the calculated average PLB cycle time depending on the number of
slaves. You can use the blue graph to determine the recommended PROFINET update time
(see "Configuration of the PN update time (Page 72)"). The orange graph shows you the
recommended minimum PROFINET/PROFIsafe watchdog time. It is specified in the
configuration tool with the PN "update time" times the "accepted update cycles without IO
data". For PROFIsafe applications, the PROFIsafe monitoring time should always be set
shorter than the PROFINET watchdog time.
Содержание SIMATIC Power Line Booster
Страница 34: ......