Siemens S7-1200 System Manual page 570

Communication
10.3 PROFIBUS
In the figure below, the S7-1200 is a DP slave to an S7-300 controller:
The S7-1200 is connected to a PROFIBUS network as a DP master with the CM 1243-5
communication module. The CM 1243-5 (DP master) module can be the communications
partner of DP V0/V1 slaves. In the figure below, the S7-1200 is a master controlling an
ET200S DP slave:
If a CM 1242-5 and a CM 1243-5 are installed together, an S7-1200 can perform as both a
slave of a higher-level DP master system and a master of a lower-level DP slave system,
simultaneously:
For V4.0, you can configure a maximum of three PROFIBUS CMs per station, in which there
can be any combination of DP master or DP slave CMs. DP masters in a V3.0 or greater
CPU firmware implementation can each control a maximum of 32 slaves.
The configuration data of the PROFIBUS CMs is stored on the local CPU. This allows simple
replacement of these communications modules when necessary.
To use PROFIBUS with S7-1200 V4.0 CPUs, you must upgrade the PROFIBUS Master CM
firmware to V1.3.
You can make this upgrade using a Secure Digital (SD) card.
Note
It is recommended that you always update the PROFIBUS CM firmware to the latest version
available (http://support.automation.siemens.com/WW/view/en/42131407) at the Siemens
Service and Support web site.
570
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG