Monitor One Instance of a Compiled CFC Block in PCS 7
A compiled CFC chart block can be inserted as an FB instance more than once, and each placed instance can be inspected in CFC online test mode. Open the chart containing the desired instance, select that block and use the CFC test-mode display to inspect its values. The s7_m_c attribute is relevant when exposing chart I/O to the OS; it is not required merely to monitor a selected block instance inside CFC.
Table of Contents
- How compilation and instances relate
- Monitor the required instance in CFC
- Expose selected chart I/O to the OS
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
How compilation and instances relate
Compiling a CFC chart as a block type creates an FB type from the chart interface and logic. Inserting that type into another chart creates an instance. Each inserted block has its own instance data and can be monitored separately by selecting the corresponding chart and block.
Monitor the required instance in CFC
- Locate the CFC chart where the required FB instance was inserted.
- Open that chart in CFC Editor and establish an online connection to the intended automation system.
- Enable CFC test mode using the command available in the installed CFC version.
- Select the particular FB instance in the chart and inspect its online parameter values and execution state.
- Repeat with another chart or instance if needed; ensure the selected online target is the intended CPU.
Expose selected chart I/O to the OS
If the requirement is to see chart I/O in WinCC OS, configure the relevant Chart I/O attributes for OS transfer, including s7_m_c where applicable in the project workflow, then compile and update the OS according to the matching PCS 7 procedure. This is distinct from CFC test-mode monitoring: an attribute that publishes data to the OS does not select which CFC instance an engineer views online.
Verification
Confirm the chart path, block type, instance name and CPU before enabling test mode. Compare the displayed online values with expected process states and check whether the block is executing. For OS display, verify the generated tag and runtime value separately.
Limitations and Operational Precautions
The cited Siemens manual is CFC V9.0 SP5; menu names and compatibility should be checked against the installed CFC version. Test mode is read-only observation unless an engineer deliberately changes values through permitted controls; do not force or modify control values without authorization and process safeguards.
Engineer FAQ
Can the same compiled CFC block type be used at three locations? Yes. Each insertion creates a separate instance in a chart, with its own instance data.
How do I monitor only the first instance? Open the chart containing that instance, go online in CFC test mode and select the specific block instance.
Do I need s7_m_c to view an instance in CFC test mode? No. That attribute is associated with OS transfer of values; online CFC monitoring is performed on the selected instance in its chart.
What does s7_m_c do in this context? The source reply describes it as an attribute used to transfer selected Chart I/O values to the OS. Confirm exact attribute handling in the matching PCS 7 version.
Does compiling a chart as a block type automatically expose all its I/O to WinCC? No. The chart interface and OS-related attributes/configuration determine what data is made available to the OS.
Can I monitor an instance without selecting the correct CPU? No. Confirm the online target and project before viewing values to avoid inspecting a different controller than intended.
What does CFC test mode show? The cited CFC manual describes online display of block and runtime-group enable states; individual instances in the chart can be inspected online.
Does monitoring prove the logic is correct? No. It shows online values and execution state. Compare them with the design requirements and expected process behavior.
Can I change values while monitoring? Any write, force or operator action depends on permissions and project controls; use site procedures and process safeguards before changing live values.
Why are OS visualization and CFC monitoring separate? CFC test mode inspects the selected engineering instance, while OS tags expose selected project data for runtime visualization and operation.