Siemens SIMATIC S7-200 System Manual page 249

Comparing Token Rotation Times
Table 7-12 shows comparisons of the token rotation time versus the number of stations, amount of
data, and the baud rate. The times are figured for a case where you use the Network Read and
Network Write instructions with the S7-200 CPU or other master devices.
Table 7-12 Token Rotation Time (in Seconds)
Baud Rate Baud Rate
Transferred
9.6 kbaud 9 6 kbaud
19 2 kbaud 19.2 kbaud
187 5 kbaud 187.5 kbaud
Understanding the Connections That Link the Network Devices
Network devices communicate through individual connections, which are private links between
the master and slave devices. As shown in Figure 7-32, the communications protocols differ in
how the connections are handled:
The PPI protocol utilizes one shared connection among all of the network devices.
-
The PPI Advanced, MPI, and PROFIBUS protocols utilize separate connections between
-
any two devices communicating with each other.
When using PPI Advanced, MPI, or PROFIBUS, a second master cannot interfere with a
connection that has been established between a master and a slave. S7-200 CPUs and EM 277s
always reserve one connection for STEP 7--Micro/WIN and one connection for HMI devices. Other
master devices cannot use these reserved connections. This ensures that you can always
connect at least one programming station and at least one HMI device to the S7-200 CPU or EM
277 when the master is using a protocol that supports connections, such as PPI Advanced.
PPI
All devices share a common
connection
PPI Advanced
MPI
PROFIBUS
Each device communicates
through a separate connection
Figure 7-32 Managing the Communications Connections
Bytes Bytes
2 3
1 0.30 0.44
16 0.33 0.50
1 0.15 0.22
16 0.17 0.25
1 0.009 0.013
16 0.011 0.016
PPI Connection
Connection 1
Communicating over a Network
Number of Masters
4 5 6 7
0.59 0.74 0.89 1.03
0.66 0.83 0.99 1.16
0.30 0.37 0.44 0.52
0.33 0.41 0.50 0.58
0.017 0.022 0.026 0.030
0.021 0.026 0.031 0.037
PPI Connection
Connection 2
Connection 1
Chapter 7
8 9 10
1.18 1.33 1.48
1.32 1.49 1.65
0.59 0.67 0.74
0.66 0.74 0.83
0.035 0.039 0.043
0.042 0.047 0.052
PPI Connection
Connection 1
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