C-14
Communications Processor CP 541
EWA 4NEB 812 6188-02
C.7
Calculating the Token Rotation Time
The token rotation time (TRT, target rotation time) specifies the time re-
quired until all active stations have had possession of the token once.
The calculation for the token rotation time is given in the following.
The token rotation time has the default 30000 bit times in DB1 of the
CP 541. You can operate SINEC L2 with this setting.
If you wish to optimize the timing of your SINEC L2, you must calculate the
token rotation time yourself. You can thus minimize the token rotation time,
which results in a speeding up of time-critical messages.
Calculate the token rotation time according to the following instructions. Bit
times are used.
The bit time is the time elapsing during sending of one bit (the reciprocal of
the transmission rate, see DIN 19245).
Step
Action
Meaning
1
Determine the number of stations in
SINEC L2.
You must take into account all active sta-
tions of SINEC L2.
Passive stations cannot send messages inde-
pendently.
2
Determine the maximum number of mes-
sages for each active station.
The number of messages is given by the
number of configured connections per sta-
tion. You must add the connections which
the station can establish by itself.
3
Distinguish the messages according to their
type, such as broadcast, PLC-PLC or DP
connection
1
).
Sort the messages according to their type.
You will have an overview of the frequency
of individual types of connection.
4
Calculate the basic load for the individual
messages without data.
Add up the values from Table C-10 accord-
ing to the frequency of individual connec-
tions.
5
Determine the total data volume.
Add up the data (number of bytes) of each
message.
6
Calculate the loading caused by data for
each message.
For each transmitted data byte, you must add
11 bit times.
7
Add up the individual loads.
–
1
If necessary, you can take the time requirement for the DB connections from the configuring tool, such as COM ET
200 Windows, which calculates the token rotation time for a pure DP system.
Meaning
Default
Optimization
Calculation
Parameters of DB1