146 SI-Ethernet User Guide
Issue: 3
7.3.1 RTMoE Message rate capability
When designing a network, the message loading for each device should be checked to ensure the
number of messages do not exceed the maximum recommended value.
Consider the following example where a Unidrive M700 is communicating with three other devices
over Ethernet using Modbus TCP/IP (10 parameters read every 100 ms), EtherNet/IP (5
parameters read every 10 ms and 5 parameters written every 10 ms) and RTMoE (2 parameters
written every 500 µs).
7.3.2 RTMoE Message type
From the system design, it should be known how many drives will be used and what data needs to
be sent where. There are two fundamental ways of sharing data:
• Cyclic data – use cyclic links for important information relating to the dynamic behavior of
the machine (e.g. control word, speed reference, etc.)
• Non-cyclic data – used for non time-critical information (e.g. drive setup data) A user
program must be used to control the transfer of non-cyclic messages. (see Non cyclic
enable (S.02.035) and Non cyclic base parameter (S.02.036))
Each cyclic message can be one of three types:
Protocol
Number of
Parameters
Rate
Parameters accessed /
second
Message rate /
second
Modbus TCP/IP 10 x read 100 ms 100 10
EtherNet/IP
5 x read 10 ms 500 100
5 x write 10 ms 500 100
RTMoE 2 x write 500 µs 4000 2000
Total 5100 2210
Maximum supported 6000 8000
Within capability?
1
Unicast – used if data needs to go
from one device to another
2
Broadcast – used if data needs to go
from one device to all other devices
3
Multicast – used if data needs to go
from one device to a subset of the other
devices
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