Resolving GRAPH Block Migration Errors from STEP 7 to TIA V19

When an S7-300/S7-400 STEP 7 V5.x project is migrated to TIA Portal V19, the migration tool typically issues a warning that GRAPH sequential function chart blocks are not fully supported. After migration, the GRAPH FBs open read-only, cannot be recompiled, and the project surfaces a follow-on warning: "This address cannot be assigned through a variable." This article documents the root cause, the two engineering-grade workarounds (GRAPH add-on install vs. STL conversion), and the steps required to clear the residual compile warnings so the migrated project is production-ready.

1. Problem Description

Two distinct but related symptoms appear after running the TIA Portal migration tool on a STEP 7 V5.x project that contains GRAPH sequence blocks:

1. GRAPH FBs become non-editable. Double-clicking a GRAPH FB in the migrated project opens the block, but the sequence editor is grayed out. Attempts to compile the program (or the block) fail with errors of the form "The block was uploaded from the S7-300/S7-400 module and cannot be edited or compiled in TIA Portal." The corresponding FB retains the Know_How_Protect attribute and the original STL/FBD source is shown as a comment-only view.
2. Address-assignment warning during compile. After working around the GRAPH block, the next full project compile produces warning W:"This address cannot be assigned through a variable", usually pointing at bit memory (M) or input (I) addresses that were wired to GRAPH step enable / acknowledge / error bits in the original program.

Both symptoms block the project from being downloaded to a real S7-300/S7-400 CPU or an S7-1500 retrofitted target.

2. Root Cause Analysis

2.1 Why the GRAPH block is read-only

STEP 7 V5.x stores GRAPH sequence blocks as compiled FBs whose interpretive data is held in a parallel *.sfc container consumed by the S7-GRAPH editor. The TIA Portal migration tool reads the STEP 7 V5.x archive (*.zip or *.arc) and emits a TIA Portal migration file (*.am20 for V19 targets) that contains the FBs as compiled STL/FBD code only. The S7-GRAPH add-on for TIA Portal reads the interpretive *.sfc metadata to reconstruct the chain step view. When that add-on is not installed in TIA Portal at the time of migration, the FB is migrated as a generic compiled block and is consequently read-only.

2.2 Why the address warning appears

In STEP 7 V5.x, the GRAPH FB exposes a parameter interface where individual M, I, Q bits are wired by absolute address rather than by symbolic tag. The TIA Portal compiler re-validates these wirings against the strict type-checked PLC tag table (introduced in V13 and tightened in V17 / V18 / V19). The result is warning W:"The address ... cannot be assigned through a variable" on every absolute wiring that was previously tolerated as a direct bit access on the GRAPH interface. The functionality is not broken; the warning is informational and signals that the FB is operating on an untyped symbol.

3. Prerequisites

Before attempting any of the workarounds, verify the following on the engineering workstation:

• TIA Portal V19 with the matching S7-GRAPH for TIA Portal option package installed (Setup detection: Start > Control Panel > Programs > TIA Portal V19 > Change > Modify Installation).
• The STEP 7 Professional V19 DVD or download package (required because the migration tool is bundled on the STEP 7 Prof DVD in the Support folder, per Siemens Support entry 58638200).
• Access to the offline STEP 7 V5.x project (the *.s7p file, not an upload). If only an upload is available, the original GRAPH chain-step data is lost and the GRAPH add-on install path will not work; STL conversion becomes the only path.
• The STEP 7 V5.4 / V5.5 / V5.6 S7-GRAPH source add-on, used in the original project (needed to match the chain-step data layout).
• Administrator rights on the engineering workstation (TIA option packages require elevated install).

4. Solution A — Install the S7-GRAPH Add-on and Re-Migrate

This is the only path that preserves the original sequence logic and is recommended for production programs.

1. Insert the TIA Portal V19 DVD or mount the ISO. Launch Start.exe and select Modify Installation.
2. In the package selection tree, expand SIMATIC S7-1500 / S7-1200 / S7-300/400 > TIA Portal Add-ons and tick S7-GRAPH. Accept the licence terms.
3. Complete the installation and restart TIA Portal V19.
4. Open the STEP 7 V5.x *.s7p project in STEP 7 V5.5 / V5.6 (this is mandatory; the migration tool is invoked from inside the V5.x project, not from TIA Portal). Per the official Siemens migration documentation, the source project is converted to a TIA Portal migration file (*.am20) which is then imported into TIA Portal V19. See Migration of STEP 7 projects (S7-300, S7-400) - TIA Portal for the canonical workflow.
5. Re-run the migration: Project > Migrate to TIA Portal > select TIA Portal V19 as the target. The dialog will now read GRAPH: full support in the component list, and the previous warning disappears.
6. Open the imported project in TIA Portal V19. Right-click the GRAPH FB and choose Open with S7-GRAPH. The chain step view must now show transitions, steps, and interlocks, not the STL stub.
7. Compile the project (Project tree > PLC > Compile > Software (rebuild all)). The cannot be assigned through a variable warning should reduce to the same address that the GRAPH interface still uses absolute on; this is resolved in step 8.
8. For every remaining warning, replace the absolute M / I / Q address on the GRAPH FB instance DB with a typed PLC tag (e.g. "Graph1_Step1_Active" of type BOOL). Re-compile. The address warning clears because the compiler now sees a typed symbolic binding instead of a direct bit access.

5. Solution B — Convert GRAPH to STL before Migration

Use this path when the STEP 7 V5.x source cannot be reopened (e.g. upload-only archive) or when the S7-GRAPH add-on licence is unavailable.

1. Open the original *.s7p in STEP 7 V5.5 / V5.6 with the S7-GRAPH add-on installed.
2. Open each GRAPH FB. From the menu, choose Options > S7-GRAPH > Generate STL Source (or right-click the FB > Generate Source > STL). The chain-step data is rendered as a structured STL program with A, S, R, L, and JC/JCN instructions for every transition.
3. Save the generated STL sources in the Sources folder of the STEP 7 project.
4. Compile the sources to produce STL-equivalent FBs (Sources > Compile). The resulting FBs no longer carry the GRAPH interpretive data and are pure STL.
5. Remove the original GRAPH FBs from the program (Delete blocks), and from any instance DB, to avoid duplicate symbol conflicts.
6. Re-run the migration to TIA Portal V19. The GRAPH not supported warning no longer fires because the project no longer contains GRAPH blocks.
7. Re-test every chain transition, every step-enable condition, and every interlock. STL conversion is one-way: comments, supervision conditions, and step names are lost; only the boolean logic is preserved.

6. Solution C — Delete and Re-Programme (Last Resort)

When neither source is available nor the GRAPH add-on can be licensed, the FBs are removed from the migrated project and re-engineered. This is the only path that ends up with a fully TIA-V19-native GRAPH chain, but it costs engineering hours and re-validation time on the target machine.

1. Open the migrated TIA Portal V19 project.
2. Delete the read-only GRAPH FBs and their instance DBs.
3. Open the calling OB (typically OB1 or a cyclic OB) and remove the FB call. Compile to confirm the project builds clean.
4. Add a new GRAPH FB (Add new block > Function block > Type: GRAPH) and re-author the chain by hand from the machine documentation.
5. Re-bind every absolute address to a typed PLC tag to avoid the cannot be assigned through a variable warning.

7. Clearing the Address-Assignment Warning

The warning "This address cannot be assigned through a variable" is a TIA Portal V19 compiler message that fires when the GRAPH FB's instance interface still carries an absolute address (e.g. M 50.0 or I 4.7) that the compiler cannot reconcile with a typed PLC tag. The corrective procedure is identical for all three solutions:

1. Open the GRAPH FB in the GRAPH editor.
2. Switch to the Interface tab.
3. For every parameter whose Address column shows an absolute address, click the cell, select Symbolic from the dropdown, and pick a typed tag from the PLC tag table.
4. If the tag does not yet exist, declare it in PLC tags > Default tag table with the correct data type (BOOL for step bits, INT / DINT for step numbers, TIME for supervisions).
5. Save, compile, and confirm the warning no longer appears in Info > Compile.

8. Verification Procedure

After applying Solution A, B, or C, run the following verification before downloading the project to a real CPU:

1. Compile clean. Project > Compile > Software (rebuild all). The output window must show zero errors. Warnings should be limited to documented intentional absolute wirings.
2. Cross-reference check. Project tree > PLC > Cross-references. Confirm that every call to the GRAPH FB resolves and that the instance DB is unique.
3. Block consistency. Project tree > PLC > Blocks > right-click > Check block consistency. All blocks should report OK.
4. Offline / online diff. With an S7-300 / S7-400 CPU online, Online > Compare offline / online. The GRAPH FB's compiled time stamp should match the source timestamp and Identical should appear in the comparison.
5. Functional test on a PLCSIM instance. Open Start > SIMATIC > PLCSIM (V19 build). Download the project to a simulated CPU. Manually step through every chain transition and confirm that steps activate, supervision timers fire, and interlocks trip as in the original V5.x program.
6. Know-how-protect check. Right-click the GRAPH FB > Properties > Protection. If the original block was know-how-protected, the Compilation property must show Protected in the migrated block; otherwise the protection has been silently stripped and the project should not leave the engineering environment.

9. Common Edge Cases and Field Notes

• Know-how-protected GRAPH FBs. STEP 7 V5.x GRAPH FBs are sometimes know-how-protected at the source. The S7-GRAPH V5.x add-on is required to open the FB even for migration; without it, the FB migrates as an opaque STL stub. Solution A still works if the S7-GRAPH V5.x add-on is installed on a parallel engineering workstation; the FB is then migrated with the protected container intact.
• GRAPH FB called from a CFC plan. If the GRAPH FB is referenced from a CFC (Continuous Function Chart) plan, the migration tool migrates CFC charts as read-only diagrams with the same uploaded from S7-300/400 lock. The CFC add-on for TIA Portal V19 must be installed; otherwise the diagram becomes non-executable and the GRAPH FB is unreachable.
• Step 7 V5.4 source on a V19 target. The TIA Portal V19 migration tool accepts STEP 7 V5.4 SP5 and later. If the source is older, upgrade the source in STEP 7 V5.5 first; the migration tool does not convert pre-SP5 archives.
• Custom GRAPH blocks outside the default range. GRAPH FBs in the user range (e.g. FB 1000+) are migrated with the same read-only behaviour. Solution A handles them identically to the default range.
• Re-importing after a failed migration. If the migration is interrupted (anti-virus quarantine, disk full), the *.am20 file is corrupt. Re-export from STEP 7 V5.x; do not attempt to repair the *.am20 archive manually.
• Migration tool location. The standalone migration tool is shipped on the STEP 7 Professional V19 DVD in the Support folder and is documented in Siemens Support entry 58638200. It can be invoked independently of TIA Portal when the source STEP 7 V5.x project must be converted to a TIA Portal migration file on a workstation that does not have a STEP 7 V5.x install.

10. Troubleshooting Matrix

11. When to Escalate to Siemens Support

Escalate to the Siemens Industry Online Support team with the following data when the migration tool itself fails (e.g. *.am20 cannot be generated, GRAPH option install fails on Windows 11 24H2, or the GRAPH block is corrupt in the source):

1. Exact TIA Portal V19 build number (Help > About).
2. Exact S7-GRAPH V19 option build number.
3. Exact STEP 7 V5.x source build number (e.g. V5.5 SP4 Hotfix 6) and S7-GRAPH V5.x build.
4. Whether the source is offline (*.s7p) or an upload.
5. The exact warning / error text in English (German original if running a German TIA).
6. The full migration log (C:\Users\<user>\AppData\Local\Siemens\Automation\<version>\MigrationLog.txt).