S7-400 412-5H Firmware 6.0 Compatibility with STEP 7 5.6 SP1

Overview

Engineers migrating legacy SIMATIC S7-400 H systems to STEP 7 V5.6 SP1 (or V5.6 SP2) frequently encounter a compatibility question that is not always explicitly documented by Siemens: does the CPU firmware have to be updated when the engineering tool is upgraded? This is especially common in plants where WinCC 7.x is being rolled forward (e.g., WinCC 7.5 SP1) and the integrated STEP 7 project has to be opened in a newer SIMATIC Manager version.

This reference covers the 6ES7 412-5HK06-0AB0 (S7-400H, CPU 412-5H, firmware 6.0) and clarifies the relationship between the CPU firmware, the STEP 7 version, and the WinCC version. The short answer, derived from the field behaviour shown in STEP 7 V5.6 SP2 hardware configuration, is that the CPU does not need a firmware upgrade solely to be opened/edited in STEP 7 V5.6 SP1. However, several preconditions, side effects, and best-practice rules apply, especially for redundant (H) systems.

Prerequisites

• Existing STEP 7 V5.5 project with S7-400H station (CPU 412-5H, MLFB 6ES7 412-5HK06-0AB0, firmware 6.0.x).
• Target installation: STEP 7 V5.6 SP1 or V5.6 SP2 on Windows 7 SP1 / Windows 10 (64-bit) with current updates.
• For WinCC integration: WinCC 7.5 SP1 (and the matching WinCC/Step 7 ES combination installed before opening any integrated project).
• SIMATIC Manager licence (Floating or Single) with valid authorsation for V5.6.
• STEP 7 V5.6 SP1 DVD or installation media. The hotfix list is documented in the corresponding Readme file shipped with the DVD.
• Full project archive (including S7 program, H station configuration, NetPro, symbol table, and any HMI/WinCC tags).

CPU Identification and Compatibility Matrix

The MLFB 6ES7 412-5HK06-0AB0 breaks down as follows:

STEP 7 V5.6 SP1/SP2 reads the programming package field from the CPU's electronic nameplate, not the firmware version, to decide which toolbox to expose. Because the 412-5H hardware release 6 has a programming package of "STEP 7 V5.2 +", any STEP 7 version from V5.2 up to and including V5.6 SP2 can open and edit the configuration without re-flashing the CPU.

STEP 7 / Firmware / CPU Compatibility (412-5H, 6ES7 412-5HK06-0AB0)

Use the Siemens Industry Online Support compatibility tool to cross-check third-party modules (IM, CP, FM) that sit on the same rack, because those modules often have a tighter coupling to STEP 7 than the CPU does.

STEP 7 V5.5 vs V5.6 SP1 / SP2 — What Actually Changes

STEP 7 V5.6 was the last "classic" STEP 7 line; it does not move to TIA Portal but adds a number of bug fixes, new CPU types, and OS support. The points that matter most for an H-system migration are:

Because V5.6 SP1 reads V5.5 projects without conversion, the CPU firmware does not have to be upgraded as a side effect of the tool upgrade. The CPU continues to run on the existing firmware while the engineering environment is refreshed.

Firmware 6.0.x Status and Update Considerations

Firmware 6.0 for the 6ES7 412-5HK06-0AB0 is a long-running release family. The 6.0.x updates are correction/robustness releases, not feature additions. The relevant decision points are:

1. Functional reasons to update: If you are seeing known firmware bugs (search the Siemens Knowledge Base for "412-5H 6.0" + symptom), updating to 6.0.9 is justified.
2. Cyber-security reasons: Firmware updates issued in the wake of advisories (e.g., SIMATIC-related ICS advisories) should be applied.
3. Compatibility with new I/O: Newer CP/IM firmware may require a minimum CPU firmware level for full diagnostic richness.
4. Redundancy behaviour: H-CPU firmware updates typically improve link-up and event-sync robustness; reading the firmware release notes is mandatory for H systems.

If the firmware is updated, follow the procedure in the SIMATIC Manager: PLC > Update Firmware. The CPU must be in STOP, the redundant partner must be in solo run (or both CPUs updated in turn to maintain redundancy), and the update file is supplied as a binary via the firmware download package in the Siemens support portal entry for the 6ES7 412-5HK06-0AB0.

WinCC 7.5 SP1 Integration

WinCC 7.5 SP1 requires a STEP 7 version that supports the integrated project navigation. The supported combinations are documented in the WinCC 7.5 SP1 release notes. In practice, the workflow is:

1. Install STEP 7 V5.6 SP1 (or SP2) on the engineering station.
2. Install the matching "SIMATIC WinCC / Step 7 ES" option (the AS-OS bridge). This is the package that lets the WinCC Explorer see the S7 symbols and connections directly.
3. Install WinCC 7.5 SP1.
4. Open the integrated project from SIMATIC Manager; the WinCC component is read-only until the version is migrated by the WinCC project migrator.

If the project was previously edited in WinCC 7.0/7.2/7.3, the WinCC 7.5 SP1 migrator performs the conversion; this is independent of the STEP 7 side.

Step-by-Step Migration Procedure

1. Pre-migration housekeeping

1. Open the project in STEP 7 V5.5 and run PLC > Check Block Consistency and Check HW Configuration. Resolve any warnings before migration.
2. Archive the entire project directory (including the global libraries and source files) using the SIMATIC Manager File > Archive function. This produces a single .zip/.arj-style container that is restorable in V5.6.
3. Document the CPU firmware version: PLC > Diagnostics/Setting > Module Information, note the Firmware field (e.g., V6.0.7).
4. Document the rack layout, CP/IM slot numbers, and the H-station link module assignments (for H systems, both rack 0 and rack 1).

2. Tool upgrade

1. Install STEP 7 V5.6 SP1 (or SP2). Do not uninstall V5.5; parallel installation is permitted but the project should be opened with the same tool version that last wrote it. V5.6 opens V5.5 projects natively.
2. Install the AS-OS Engineering option that matches the WinCC version (7.5 SP1 in this scenario).
3. Install WinCC 7.5 SP1.
4. Reboot. Verify that the SIMATIC Manager help screen shows STEP 7 V5.6 SPx and that the licence key is recognised.

3. Open and re-save the project

1. Launch SIMATIC Manager (V5.6 SP1).
2. Open the archived project from the de-archived location. SIMATIC Manager will display the V5.5 project without prompting for conversion.
3. For each S7-400H station, double-click HW Config. The CPU is loaded into the catalogue as a 6ES7 412-5HK06-0AB0 with firmware 6.0.0 (or whatever is current in the installed catalogue) — the CPU's running firmware is unchanged.
4. Click Station > Save and Compile. No download is performed at this point.
5. Open the WinCC component (if integrated). Confirm that the symbol resolution works and that the HMI tags still reference the correct DBs.

4. Validation (offline)

1. Run PLC > Check Block Consistency on every S7 program under the H station. Look for SFCs/SFBs that may have changed call interface (rare between V5.5 and V5.6, but possible for newly inserted H-functions).
2. Run NetPro > Check Consistency for the entire project. Resolve any subnet errors.
3. If you intend to update CPU firmware, do it in a planned outage. Otherwise, skip to step 5.

5. Download (optional)

1. Connect the engineering station to the plant network.
2. Download HW Config to the standby CPU of the H-pair. The active CPU remains in RUN; H-system takes care of the role switch automatically.
3. Download the program blocks to the standby CPU. Wait for synchronisation. Switch roles and repeat, or use the H-system "Update both CPUs" sequence supported by the H-CPU option.

H-CPU Specific Considerations

The 412-5H is a redundancy CPU. Beyond the normal S7-400 migration steps, the H-CPU option (sometimes called the "H-CPU support" or "S7H" package) must be installed in SIMATIC Manager. Without it, the H station will not be editable.

Verification

After the migration and any downloads, verify the following:

1. Module Information > Firmware still reports the original version (e.g., V6.0.7) on both H-CPUs if you did not deliberately flash.
2. Diagnostic buffer on both CPUs: no new SF (system fault) entries related to the migration; the last event should be the planned role switch or a normal start-up event.
3. Synchronisation status: H-CPU diagnostic screen reports "LINK OK" on both pairs and "SYNC" green.
4. WinCC tag resolution: in WinCC Explorer, open a tag that references a DB from the S7 program; the address must resolve and the value must update on a forced bit change.
5. NetPro consistency: re-run the check, the result must be "No errors".

Troubleshooting Matrix

Best-Practice Notes

• Keep the CPU firmware at the latest 6.0.x patch level where the plant's risk window allows. The firmware update is a one-time, low-risk operation when scheduled against a planned outage.
• Always run the Siemens compatibility tool for the entire rack, not just the CPU. CP 443-1, IM 460/461, and FM modules have their own firmware/version constraints.
• Maintain at least one engineering station that remains on STEP 7 V5.5 for emergency troubleshooting of legacy projects that have not yet been migrated. The two versions can co-exist on different machines.
• For H systems, treat firmware updates as a maintenance procedure, not a routine: capture the H statistics, perform a planned role swap test after the update, and archive the diagnostic buffer of both CPUs.
• Document the engineering tool version in the plant asset record. Many "missing CPU" problems on older H systems are actually "wrong STEP 7 installed on the only available laptop".

FAQ