Distribution Of The Target Rotation Time - Siemens SIMATIC S5 Manual

S5-95U, SINEC L2
Each station measures the "real" rotation time and calculates the difference between target rotation
time and "real" rotation time (= token hold time). During this time, a station can transmit: first,
the frames with high priority, then the frames with low priority. When the token hold time is used
up, the station must pass the token to the next station.
Actual token rotation time used up by the
other stations
Station relinquishes
the token
Figure 1-4. Distribution of the Target Rotation Time (1)
If the transmitter has no token hold time at its disposal (see Figure 1-5), it can only transmit one
frame with high priority before is has to pass the token.
Actual token rotation time used up by the other stations
Station relinquishes
the token
Figure 1-5. Distribution of the Target Rotation Time (2)
Broadcasting
Broadcasting is when an active station sends a message frame to all active and passive stations.
Multicasting
Multicasting is when an active station sends a message frame to several active and passive
stations.
EWA 4NEB 812 6112-02
Target rotation time
Remaining token rotation time
Station receives
the token again
Target rotation time
Station receives
the token again
Station transmits all high-
priority and low-priority
message frames
Station relinquishes the
System Description
token
Station
transmits a
high-priority
message frame
Station relinquishes
the token
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