How OB35 Timing and Process Image Updates Work in PCS 7
OB35 is a cyclic interrupt organization block scheduled at its configured interval; its execution time is the CPU time spent running its code, not a capacity allocation added to the OB1 cycle. OB1 runs as the normal cyclic program and can be interrupted by cyclic interrupt OBs. To have process-image I/O updated for the OB35 task, assign a process image partition to OB35 and assign the relevant module addresses and channel blocks to that partition.
Table of Contents
- Interval and execution time are different
- Process image behavior
- Assign a process image partition
- What happens when an interrupt occurs
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
Interval and execution time are different
The configured OB35 interval sets when the cyclic interrupt is called. Execution time is how long the CPU takes to process that invocation. If OB35 work exceeds its interval or competes with higher-priority work, CPU interrupt and cycle monitoring behavior matters; do not infer schedulability from the interval alone.
Process image behavior
PCS 7 Compendium Part A V9.0 explains that the process image is normally updated by OB1. When process image partitions are configured, the associated cyclic interrupt OB updates its assigned partition. Without a partition assigned to OB35, cyclic logic can run using values last updated during OB1 rather than receiving an OB35-synchronous I/O update.
Assign a process image partition
- In CPU properties, assign an available process image partition to the required cyclic interrupt OB, such as OB35.
- In the hardware configuration, assign the relevant I/O module addresses to that same partition.
- Place corresponding channel blocks in the runtime OB associated with the partition.
- Compile and verify the hardware and CFC configuration before download. The available partitions and OB timings depend on CPU and project configuration.
What happens when an interrupt occurs
A cyclic interrupt can preempt lower-priority execution such as OB1, and the CPU resumes interrupted lower-priority work when the interrupt OB completes. This does not provide a separate execution resource or independent CPU capacity. Evaluate total CPU load and configured priorities/timing using the applicable CPU documentation.
Verification
Check the configured OB35 interval and assigned process image partition, then verify that module addresses and channel blocks use the same partition. Use runtime diagnostics and CPU execution data to confirm that processing meets the required timing.
Limitations and Operational Precautions
Confirm version applicability and operational impact before changes to a running control system. Use approved backup, testing, change-control and rollback procedures.
Engineer FAQ
How are PCS 7 OS areas created? PCS 7 derives OS areas from the configured picture hierarchy; the PCS 7 V9.0 manual maps the second Picture Tree Manager level to OS areas for user rights.
Can a client create its own unrelated area hierarchy? The OS client editor configures visible areas and rights from the OS picture structure; it does not replace the engineering hierarchy as the source.
What does an empty CSV export prove? Only that the generated file has headings but no rows; it does not reveal whether the cause is filtering, project data, or an export defect.
Can an installer compatibility bypass establish support? No. A successful setup launch does not prove that a software and operating-system pairing is tested or supported.
Does PCS 7 V8 license entitlement automatically cover V9? The applicable license and upgrade entitlement must be checked for the exact product and contract; do not infer it from version numbering.
Does local mode bypass all motor stops? No. Mode selection and interlocks or stop inputs are separate logic conditions; inspect the exact block version and signal states.
How does PCS 7 treat cyclic interrupt process images? A process image partition assigned to a cyclic interrupt OB is updated when that OB runs; without such assignment, the regular OB1 update may leave cyclic logic using older values.
Can several PDL pictures appear in one WinCC screen? Yes. WinCC picture-window objects can display project PDL files; PCS 7 APG V9.0 SP2 also documents a four-quadrant display.
Should APG Quad Screen be assumed present in every project? No. Confirm the installed APG release and compatibility with the project's PCS 7 and APL versions.
When should an issue be escalated? Provide exact product versions, project context, reproducible steps, and relevant logs or configuration evidence with private details removed.