200plc does not support the main station. 300plc supports the main station. What does it mean?

200plc does not support the main station. 300plc supports the main station. What does it mean?
Please give an example. Thank you.

1. In MPI, PROFIBUS-DP protocol communication, are master, slave structure. For a S7-200 is not a communication master site:
S7-200CPU can only do MPI slave station, that is, between the S7-200CPU can not communicate with each other through MPI network, can only communicate with each other through PPI.
In PROFIBUS-DP protocol communication, because the S7-200 (m277) can only serve as the slave station, so the two em277 cannot communicate. However, a PC can be used as the main site to access several connected em277.
2, S7-300PLC support main site?
In MPI, PROFIBUS-DP protocol communication, are master, slave structure. That is, a main station carries several slave stations. S7-300/400plc can be used as the main station in MPI and PROFIBUS-DP protocol communication.

When S7 200 communicates with S7 300, S7 200 can only serve as the slave station, and S7 300 can serve as the main station.

In communications between 200 and 300, 300 and 400 can be used as the master site, while 200 can only be used as the slave site.
For example, the use of PROFIBUS-DP communications, 300, 400 settings for the main station, and 200 + em277 as the slave station for CPU communication.

1. When you use different communication protocols, the s7200plc can be used as the master station or slave station.
For example, when the S7-200 CPU is reading and writing other S7-200 CPU data (using the PPI protocol) as the main site (the PPI main site can also accept data access from other main stations ); the S7-200 can also act as the main station through additional extended communication modules.

S7-200 CPU use free port communication mode, both can be the master station, but also can do from the station. For example, when the S7-200 uses the USS protocol to control the Siemens drive device, it is the main station; when using the Modbus RTU slave station command library, it is the slave station. This indicates that the master and slave nodes are determined by the communication protocol. when preparing the communication protocol, you define the roles of each communication device in the communication activity.

2. Similarly, the PLC can be used as either the master station or slave station.
3. When 200 and 300 PLC communicate with each other, the communication protocol between them is PROFIBUS, PPI, 200 as the main station, and can only be used as the slave station.

4. For details, refer:
Siemens S7-200 logo! · Sitop reference beta version 0.94

Http://www2.ad.siemens.com.cn/Download/Upload/AS/application/A0136.chm