How to Verify PCS 7 and STEP 7 Online Programs Before Editing an AS

Before editing or downloading to an automation system that is part of a PCS 7 project, compare the AS program with the engineering project. For PCS 7 CFC/SFC content, use the CFC timestamp comparison and investigate any mismatch; for conventional STEP 7 blocks, use an online/offline block comparison. A PG can load program blocks to a CPU when the configured access path and permissions allow it, so project membership alone does not prove that the offline project is current.

Why an AS in a PCS 7 project can still differ from the CPU

A PCS 7 multiproject records an engineering configuration, while the AS executes a loaded program. Classic STEP 7 also supports online work with a PLC and program downloads from the PG/PC. Therefore, loading blocks outside the normal PCS 7 chart workflow can leave the stored project out of step with the CPU. Do not infer that an AS is synchronized merely because it appears in SIMATIC Manager or communicates with PCS 7.

Siemens' current PCS 7 guidance says to download PCS 7 charts through the selected chart folder or the CFC/SFC Editor, rather than directly from the SIMATIC Manager block folder. This is a workflow rule for PCS 7 chart-based content; conventional LAD/FBD/STL blocks may require the STEP 7 comparison workflow.

Method 1: Check the PCS 7 CFC/SFC download state

Use this for program content engineered as PCS 7 CFC or SFC charts.

Open the correct PCS 7 project and the chart folder for the target AS. Confirm the project identity and the CPU you intend to inspect before going online.
Open a chart in the CFC Editor and select PLC > Compare.
Compare the timestamps for the last download-relevant change, last compilation and compilation of the downloaded program. Siemens documents the current configuration as downloaded when the last-compilation timestamp equals the downloaded-program timestamp and the last download-related change predates those timestamps.
If the timestamps do not meet that condition, treat the project and online program as potentially different. Identify what changed and where it came from before editing or downloading; the timestamp comparison indicates state mismatch but does not, by itself, identify an author or explain each code change.
Repeat the check for each relevant AS. A chart-folder status symbol can also indicate that the current configuration has not been downloaded, but inspect the comparison before drawing a conclusion.

Do not immediately perform a full or changes-only download to make timestamps match. Siemens notes that complete downloads can switch a CPU to STOP in applicable conditions and that a full download can overwrite values changed online. Establish the change scope, operational state and approved recovery plan first.

Method 2: Compare conventional STEP 7 blocks online and offline

Use this when the controller contains LAD/FBD/STL blocks that are not represented by the CFC/SFC charts you are reviewing.

In SIMATIC Manager, select the relevant online and offline block folders or the individual blocks. Confirm that both views refer to the same CPU and intended project copy.
Select Options > Compare Blocks and choose ONLINE/offline comparison. In the STEP 7 V5 manual, the detailed comparison options include executing code comparison and optionally including system data blocks (SDBs). Select the comparison scope needed for the engineering question.
Review the Compare Blocks - Results dialog, then use Details or Go to for block properties and differences. STEP 7's block comparator can compare interfaces and code; when source blocks use different languages, the comparison is based on STL.
Record and resolve every relevant difference with the responsible project owner before editing. A comparison identifies differences; it does not determine which version is correct or whether downloading it is safe.

Exact menu labels and comparison behavior can vary by STEP 7 edition. Use the manual and online help matching the installed classic STEP 7 version. Do not use a CFC timestamp result as a substitute for comparing unrelated conventional blocks.

What an online/offline comparison does and does not prove

A matching PCS 7 timestamp is evidence that the configured compilation corresponds to the loaded program under the documented timestamp conditions. A block comparison provides a more direct view of selected block differences. Neither method proves who performed a prior download, whether a safety-related project signature is valid, that all project objects were compared, or that a chosen version is functionally correct. Select the comparison scope carefully and use the required safety-program signature checks where fail-safe functions are present.

Verification

Before changes begin, confirm the target CPU identity, selected PCS 7 project and block/chart scope. For CFC/SFC, verify the timestamp relationship in PLC > Compare. For conventional STEP 7 code, review the online/offline Compare Blocks results, including code comparison for affected blocks. Resolve unexplained differences and preserve a known-good project backup before any download. After an approved change, repeat the applicable comparison and verify the observed process behavior through the site's commissioning or change-control checks.

Limitations and Operational Precautions

PCS 7 timestamp comparison and classic STEP 7 block comparison serve related but different purposes. The cited PCS 7 timestamp procedure is documented in the V10.0 Compendium Part A; projects on earlier PCS 7 releases must follow their own installed-version documentation. The block-comparison procedure cited here is from Siemens' STEP 7 programming manual (05/2010), so confirm paths and options in the target STEP 7 edition. Do not download, read back or overwrite CPU content merely to remove a mismatch: full downloads, parameter read-back and online changes can affect process behavior or project state. Coordinate with operations and use the site's tested backup and rollback procedures.

Engineer FAQ

A PG/PC can be used for STEP 7 online operations and downloads when the CPU is reachable and access is authorized. A PCS 7 project listing is not a synchronization guarantee. Compare the correct online and offline content before editing, and treat mismatches as unresolved until their origin and intended state are established.

Technical References

Siemens, Compendium Part A – Configuration Guidelines (PCS 7 V10.0), Configuration Manual A5E52549861-AA (04/2025), §10.2 “Downloading the user program,” timestamp comparison: https://cache.industry.siemens.com/dl/files/276/109988276/att_1327441/v2/pcs7_compendium_part_a_en-US_en-US.pdf
Siemens, Programming with STEP 7, Manual A5E02789666-01 (05/2010), §9.3.5 “Comparing Blocks”: https://cache.industry.siemens.com/dl/files/107/45531107/att_91661/v1/S7pr___b.pdf