Specifications

Setting Up Communications Hardware and Network Communications
7-42
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
As a general rule, you should set the highest station address on all masters to the
same value. This address should be greater than or equal to the highest master
address. The S7-200 CPUs default to a value of 31 for the highest station address.
Token Rotation
In a token-passing network, the station that holds the token is the only station that
has the right to initiate communication. Therefore, an important performance figure
for a token-passing network is the token rotation time. This is the time required for
the token to be circulated to each of the masters (token holders) in the logical ring.
In order to illustrate the operation of a multiple-master network, consider the
example shown in Figure 7-28.
The network in Figure 7-28 has four S7-200 CPUs, and each has its own TD 200.
Two CPU 224 modules gather data from all the other CPUs.
Note
The example provided here is based on a network such as the one shown in
Figure 7-28. The configuration includes TD 200 units. The CPU 224 modules are
using the NETR and NETW instructions. The formulas for token hold time and
token rotation time shown in Figure 7-29 are also based on such a configuration.
COM PROFIBUS provides an analyzer to determine network performance.
TD 200
Station 9
TD 200
Station 7
TD 200
Station 5
TD 200
Station 3
CPU 222
Station 2
CPU 222
Station 4
CPU 224
Station 6
CPU 224
Station 8
Figure 7-28 Example of a Token-Passing Network