Lenze E84AYCER - Internal Switch Latency

Lenze · E84AYCER communication module (PROFINET) · EDS84AYCER EN 3.0 - 02/2019 20
Technical data
Internal switch latency
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4.5 Internal switch latency
The integrated 2-port switch causes runtime delays which can be calculated as follows:
Example :
20 process data words + 4 PROFIsafe words => 48 bytes
• ((36 permanent bytes + 48 bytes) x 8 x 10 nsec) + 4 μsec
• (84 bytes x 8 x 10 nsec) + 4 μsec
• 6.72 μsec + 4 μsec = 10.72 μsec
In accordance with the PROFINET specification, the shortest PROFINET I/O frame must have a data
length of 72 bytes. If the 36 permanent bytes are subtracted from the 72 bytes, 36 bytes are avai-
lable for process data. If now less than 36 bytes of process data are used, the PROFINET I/O frame is
filled with "zero bytes" until it can be transmitted. As a consequence for the calculation formula, the
shortest PROFINET I/O frame with 18 process data words (36 bytes) has always the same length and
thus the runtime delay is the same, too.
Runtime delay = ((36 permanent bytes + process data in bytes) x 8 x 10 nsec) + 4 μsec
 Note!
The use of external switches can also lead to runtime delays. Depending on the system
constellation, it may be useful to create a star topology or a line/mix topology.
Network topology
( 26)