Siemens CPU 31 Series Technical Data Manual page 89

In contrast to S7-400 CPUs, the S7-300 CPUs data only allow data access from an OP / TP
(monitor and modify functions) at the scan cycle check point (Data consistency, see the
Technical Data). Processing of the user program is not interrupted by the monitor and modify
functions.
Extending the cycle time
Always make allowances for the extension of the cycle time of a user program due to:
• Time-based interrupt processing
• Process interrupt processing
• Diagnostics and error processing
• Communication with PGs, Operator Panels (OPs) and connected CPs (for example,
• Testing and commissioning such as, e.g. status/controlling of variables or block status
• Transfer and deletion of blocks, compressing user program memory
• Write/read access to the MMC, using SFC 82 to 84 in the user program
• Ethernet communication via integrated PROFINET interface
• PROFINET CBA communication by means of the PROFINET interface (system load,
• PROFINET IO communication via PROFINET interface (system load)
CPU 31xC and CPU 31x, Technical Data
Manual, 01/2006 Edition, A5E00105475-06
Ethernet, PROFIBUS DP)
functions.
SFC call, updating on the cycle control point)
Cycle and reaction times
5.2 Cycle time
2
3
4
5
5-3