Siemens SIMATIC S7-200 System Manual page 252

S7-200 Programmable Controller System Manual
For example: Consider a network running at 9.6 kbaud with four TD 200s and four S7-200s, with
each S7-200 writing 10 bytes of data to another S7-200 every second. Use Table 7-12 to calculate
the specific transfer times for the network:
4 TD 200 devices transferring 16 bytes of data =
4 S7-200s transferring 10 bytes of data =
Total token rotation time =
To allow enough time for this network to process all requests during one token rotation, set the
HSA to 63. (See Table 7-14.) Selecting a target token rotation (1.89 s) that is greater than the
maximum token rotation time (1.29 s) ensures that every device can transfer data on every
rotation of the token.
To help improve the reliability of a multi-master network, you should also consider the following
actions:
Change the update rate for the HMI devices to allow more time between updates. For
-
example, change the update rate for a TD 200 from "As fast as possible" to "Once per
second."
Reduce the number of requests (and the network overhead for processing the requests) by
-
combining the operations of Network Read or Network Write operations. For example,
instead of using two Network Read operations that read 4 bytes each, use one Network
Read operation that reads 8 bytes. The time to process the two requests of 4 bytes is much
greater than the time to process one request for 8 bytes.
Change the update rate of the S7-200 masters so that they do not attempt to update faster
-
than the token rotation time.
238
0.66 s
0.63 s
1.29 s