Technical data

Basics of Designing a Program Structure
4.2 Blocks in the User Program
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 109
Programming OB90
The run time of OB90 is not monitored by the CPU operating system so that you can program
loops of any length in OB90. Ensure that the data you use in the background program are
consistent by observing the following when programming:
• The reset events of OB90 (see the "System Software for S7-300 and S7-400, System and
Standard Functions" Reference Manual)
• The process image update asynchronous to OB90.