5-12
Communications Processor CP 541
EWA 4NEB 812 6188-02
Before being able to calculate the cycle times for receiving and sending, you
must carry out the following actions:
Step
Action
Meaning
1
Sort the messages according to message
direction.
To calculate the local cycle time, you need
to separate the send and receive messages.
2
Establish the number of data to be trans-
mitted for each message.
With safety-related messages, take into ac-
count the 4 bytes for data security.
3
Determine the transit time for each message.
The message transit time is given by the ba-
sic load of 44 ms plus 2 ms per byte.
4
Sort the messages according to size.
–
Calculate the message transit times as follows:
Message transit time = basic load + (number of net data plus 4 bytes for data security over safety-
related data paths) x 2 ms
where: basic load = 44 ms
Calculate the local cycle time for receiving as follows:
Step
Action
1
Draw up a simple table with two rows and the number of columns corresponding to the re-
ceive messages.
Mark the first row “Receive” and the second row “Send”.
2
Enter in the “Receive” row the transit times of all possible receive messages in descending
order.
3
Then enter in the “Send” row the transit times of all possible send messages.
If you have fewer send than receive messages, you must complete the “Send” row, start-
ing with the longest send message, until the same number of send and receive messages
has been entered.
If you have no send messages, do not make an entry. For receive messages whose transit
times are shorter than UPDL, you must use the configured value for UPDL.
If you have more send than receive messages, delete all excessive send messages start-
ing with the last, shortest send message.
4
You obtain the local cycle time for receiving by adding up all the message transit times in
the completed table.
Preparing the
Calculation
Message Transit
Time
Local Cycle Time
for Receiving
CP 541 with S5-95F/S5-115F
