Synchronous Operation - Siemens SIMATIC S7-300 Reference Manual

Special Signal modules
5.4.1

Synchronous Operation

Note
The basics of synchronous operation are described in a separate manual.
Hardware requirements
For the synchronous operation of the SM 338, you require:
• CPU which supports clocked operation
• DP master which supports the equidistant bus cycle
• Slave interface (IM 153-x) which supports synchronous operation
Characteristics
Depending on the system parameterization, the SM 338 works in either
non-synchronous or synchronous mode.
In synchronous operation, the data exchange between DP master and SM 338 is
synchronous to the PROFIBUS DP cycle.
In synchronous operation all 16 bytes of the checkback interface are consistent.
If synchronicity is lost due to faults or failure or delay of Global Control (GC), the
SM 338 goes back into synchronous operation in the next cycle without error
response.
If synchronicity is lost, the checkback interface is not updated.
5-8
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03