Resolving TIA Portal V13 S7-300 Download Comparison Errors

Problem Overview

A field engineer reports the following reproducible behavior on a SIMATIC S7-300 CPU 313C programmed with TIA Portal V13 (no Service Pack):

1. The original project backup is lost; only the program resident on the PLC remains as the reference.
2. A new project is created and the CPU is brought online.
3. After the download, Go online succeeds, but the Online/Offline comparison reports differences in every block (OB1, FB, FC, DB).
4. Monitoring is blocked; TIA Portal refuses to display the online view because the blocks are flagged as different.
5. The HW configuration message "PC HW configuration has changed but has not been compiled nor charged. Diagnosis may be inconsistent or erroneously displayed" appears in the lower status bar with timestamp 17/04/2016 12:35:38.

This article is a field-proven procedure for separating the real failure modes from the cosmetic ones, and for restoring a clean Online/Offline state without losing the runtime program.

Affected Components and Versions

Root Cause Analysis

Three independent root causes can each produce the symptom of a persistent Online/Offline difference after a download. All three are present in the reported case.

Root Cause 1: Time-Stamp-Based Comparison in TIA V13

TIA Portal performs the Online/Offline comparison by comparing the block time stamps stored in the offline project against the time stamps held in the CPU's load memory. A difference in time stamps is a sufficient condition for TIA Portal to mark the block as different, even when the compiled code is bit-identical.

When the project was created from scratch and the CPU's online blocks were uploaded, the time stamps differ by definition (online timestamp ≠ offline timestamp). The Detailed comparison window shows the logical networks as green ("identical"), but the high-level status still reports a difference. This is correct TIA behavior, not a fault.

Root Cause 2: Incomplete Compile Before Download

If Compile > Software (rebuild all blocks) is not executed immediately before the download, the binary image in the project tree may not match the most recent offline source. The status bar warning "Go online: HW configuration of PLC_1 has changed but has not been compiled nor loaded" is the diagnostic signature.

For a download to proceed cleanly, both of the following must be true:

• PLC_1 > Program blocks > right-click > Compile > Software (rebuild all blocks) returns with no errors.
• PLC_1 > right-click > Compile > Hardware configuration returns with no errors.

Root Cause 3: Partial / Single-Block Download

The download action is scoped by the selection in the project tree at the moment the download button is pressed:

Partial downloads are the most common origin of the reported symptom in V13, because the time stamps of the previously loaded blocks are not aligned with the newly loaded block, and the comparison engine (V13 baseline) flags the whole station.

Pre-Download Verification Checklist

Run the following checks before any download. Each check has a pass criterion and a remediation if it fails.

1. IP / Address verification – Open Online > Accessible nodes and confirm the CPU's actual IP/MPI/PROFIBUS address matches the PG/PC interface assignment and the value in PLC_1 > Properties > PROFINET interface / MPI/DP interface. Mismatch produces a download dialog that "looks correct" but writes to the wrong node.
2. CPU protection level – In PLC_1 > Properties > Protection > CPU protection level, confirm that the protection is not set to "No access (complete protection)" and that any required password is known. A forgotten password blocks write access and is reported as a generic authorization error.
3. Operating mode – Set the CPU mode selector to RUN-P (or use the online panel Operating mode > RUN-P). RUN mode allows monitoring but blocks block deletion and partial download.
4. Project tree selection – Make sure the station node PLC_1 is selected before pressing the download button. Selecting a single block performs a partial download.
5. Compile state – Run PLC_1 > right-click > Compile > Software (rebuild all blocks) and Compile > Hardware configuration. Both must complete with 0 errors / 0 warnings on the compile log.

Step-by-Step Resolution Procedure

Step 1 – Capture the current PLC program as a safety backup

1. In TIA Portal, navigate to Online > Upload from device (software).
2. Select the CPU type (S7-300 / CPU 313C) and confirm the target PG/PC interface.
3. Choose "Upload to a new project" and store the result in a dedicated backup folder.
4. Open the new project, right-click the CPU and verify that Online > Online & diagnostics is reachable without any difference warnings.

Step 2 – Force a full compile

1. Select PLC_1 > Program blocks.
2. Right-click > Compile > Software (rebuild all blocks).
3. Open the Compile log in the inspector window. Resolve every entry marked as Error. Warnings are tolerable if they were present before the operation.
4. Select PLC_1 > Device configuration, right-click > Compile > Hardware configuration. The log must show "0 errors".

Step 3 – Execute a full station download

1. Select the PLC_1 node in the project tree (not a child block).
2. Click Download to target device in the toolbar, or right-click PLC_1 > Download to > target device.
3. In the Extended download to device dialog, confirm the PG/PC interface type (TCP/IP or PROFINET) and the target address.
4. Use "Show accessible nodes" to verify the destination CPU before continuing.
5. Choose "Download all (hardware and software)" – this is the option that aligns the station-level time stamps and resolves the V13 comparison bug.
6. Confirm the overwrite prompt for any blocks that already exist on the CPU.

Step 4 – Re-run the Online/Offline comparison

1. Right-click PLC_1 > Online > Go online.
2. Open Online > Compare > Online/Offline.
3. Each block should now show status "Identical". Time stamps in the detailed view will match the offline project.
4. Open OB1 and confirm that monitoring is available; symbols will appear as %IW0, %MW0 addresses rather than fully symbolic names – this is correct S7-300 behavior, not an error.

TIA Portal V13 SP1 Update 8: Why the Upgrade Matters

The TIA Portal V13 baseline contains a known defect in the Online/Offline compare engine that affects S7-300 targets. The defect manifests as a permanent difference status even when the Detailed comparison shows all networks green. Siemens addressed the issue in V13 SP1 and continued to refine it through subsequent Updates. Update 8 is the stable V13 line endpoint.

Reference the official Siemens support pages for the latest patches:

• TIA Portal V13 SP1 – What's new and download
• TIA Portal V13 SP1 Update 8 trial download entry
• STEP 7 V13 SP1 / TIA Portal V13 SP1 manual collection

If the customer machine cannot be upgraded, apply the workaround described in Step 3 (full station download) – it forces a re-alignment of all block time stamps and side-steps the compare bug.

S7-300 Specific Online Limitations

When an S7-300 target is brought online, the following differences from S7-1200/1500 are expected and are not symptoms of a download failure:

Operators migrating from S7-1200/1500 frequently misinterpret the lack of symbolic online data as a download failure. Validate online functionality by toggling a known input (e.g., %I0.0) and observing the corresponding output in the watch table before assuming the download is bad.

Diagnostic Buffer and Error Codes

Always inspect the CPU diagnostic buffer after a failed download. The most relevant entries for the reported case are:

Open the diagnostic buffer with PLC_1 > Online & diagnostics > Diagnostic buffer. Sort by Time descending to see the most recent events first.

Troubleshooting Matrix

Field-Commissioning Best Practices

1. Always maintain a known-good backup on an engineering share. Use Project > Archive (or File > Archive in older builds) to produce a single-file archive after every change.
2. Use version control – pair TIA Portal with a Git or TIA-specific version control plugin. The S7-300 is often deployed for 10+ years; manual backup discipline fails over that horizon.
3. Document PG/PC interface assignments in the project documentation. PN, MPI and PROFIBUS each have their own dialog in the Windows Control Panel ("Set PG/PC Interface").
4. Avoid partial downloads in production. Reserve them for diagnostics and only on a machine that can be safely re-loaded.
5. Schedule a periodic consistency check – once per quarter, perform a full Upload from device, open the resulting project, and compare it to the offline reference. A divergence here is the earliest indicator of a corrupted block.
6. Use the CPU clock – the diagnostic buffer uses the CPU clock. Set it via Online & diagnostics > Set time so that future field service has a coherent timeline.

Verification After Repair

Use the following gate checks before signing off the repair:

1. Right-click PLC_1 > Online > Go online – status must be "Connected" with no comparison warnings in the status bar.
2. Open Compare > Online/Offline – every block row reads "Identical".
3. Open OB1 online and confirm that the Monitoring on/off button is enabled and that toggling a real input changes a tag in the watch table within one scan.
4. Open the diagnostic buffer; the most recent download event has Event ID 0x4300-class (download completed) with no follow-up error event.
5. Power-cycle the CPU (MRES not required) and confirm that it returns to RUN within the configured startup time (typically 3–5 s for 313C).

Edge Cases and Operator-Specific Notes

• Know-how-protected blocks cannot be re-compiled offline. If the lost source contained protected blocks, only a re-import from the OEM restores the program fully. A round-trip via Upload from device produces a working copy that runs, but the source comments and symbols are missing.
• Multi-language TIA installations sometimes show the warning text in Spanish ("la configuración HW de PLC_1 ha cambiado pero no se ha compilado ni cargado. Es posible que el diagnóstico visualizado sea incoherente o erróneo") or German – the message is identical and the fix is identical.
• Two engineers on the same project – the online time stamps reflect the CPU clock. If two PGs download within the same minute, the Detailed compare can be confusing; this is a cosmetic issue, not a fault.
• CPU in STOP after failed download – if the download was interrupted (network glitch, MRES), perform a full Download to target device with the CPU in STOP, then return it to RUN-P.

Related Engineering Documentation

• TIA Portal V13 SP1 – Release notes and download
• STEP 7 / TIA Portal V13 SP1 manual collection
• S7-300 CPU 31xC technological functions manual
• S7-300 Automation System – Module specifications