How to Resolve Textual Interconnection Warnings After Replacing a CPU in PCS 7

To resolve "textual interconnection" warnings during CFC chart compilation after replacing an S7 controller (such as upgrading from CPU 414-2DP to CPU 416-2DP), realign the hardware I/O address symbols and execute Close Textual Interconnections. Textual interconnections are created automatically by the CFC editor as a safety mechanism when physical I/O addresses, symbol table entries, or cross-chart targets are missing from the newly inserted CPU's configuration. Because the editor refuses to silently delete your engineering logic, it converts broken hardware links into open textual strings displayed in yellow. The resolution requires restoring matching I/O addresses in HW Config, verifying the Symbol Table, closing textual links, and regenerating module drivers.

Mechanics of Textual Interconnections in the PCS 7 CFC Editor

In SIMATIC PCS 7, connections between technological blocks and hardware field devices operate through the S7 Symbol Table and Hardware Configuration (HW Config):
- Direct Symbol Binding: When an analog channel driver (e.g., Pcs7AnIn) is wired to field sensor PI_101, CFC links the block pin to input word IW 512 based on the symbolic name defined in the Symbol Table.
- The Textual Preservation Mechanism: If an engineer deletes a CPU, exchanges a controller in HW Config, or copies charts into another S7 program where the symbol or address does not yet exist, CFC does not sever the link.
- Visual Indicator: Instead, the connection line changes to a yellow margin connector containing the literal text string of the target (e.g., "Plant1/Feed/PUMP_101.Run" or "IW512"). This is a Textual Interconnection.
- Compilation Warning: During compilation, the compiler warns: Warning: Textual interconnection 'IW512' cannot be resolved. If left open, the block input defaults to its static initial value, leaving field devices unread.

Why CPU Hardware Replacement Breaks I/O Interconnections

When upgrading or replacing an S7 CPU (for example, swapping an older CPU 414-2DP for a larger CPU 416-2DP or CPU 410-5H):
1. Rack Insertion and Address Offsets: Inserting a new CPU or re-assigning DP/PN master systems frequently resets default I/O start addresses on peripheral racks (e.g., moving an analog input module from IW 512 to IW 1024).
2. Missing Symbol Table: If the S7 Program folder under the new CPU was created as an empty container, the original project's Symbol Table (Symbols) containing tag names and comments was not copied over.
3. Process Image Partition (PIP) Discrepancies: Advanced Process Library channel drivers require assignment to specific Process Image Partitions (e.g., TPA1 for cyclic execution in OB35). A new CPU configuration defaults to Process Image Partition 0 (OB1), causing the driver generator to reject channel mappings.

Locating Unresolved Links via Chart Reference Data and Logs

To pinpoint exactly which blocks and charts contain open textual interconnections:
1. Open SIMATIC Manager and double-click any CFC chart.
2. From the top menu, select Options -> Reference Data -> Display.
3. In the Reference Data window, select Textual Interconnections.
4. The system displays a comprehensive tabular list showing:
- Chart name
- Block name and parameter pin
- Missing target string / address
- Connection status (Open or Resolved)
5. Alternatively, open the compile log (Chart -> Compile -> Display Log), click the Warnings tab, select the textual warning, and click Go To to jump directly to the flagged block in CFC.

Method: Step-by-Step Restoration and Address Realignment

Follow this engineering workflow to restore all hardware links and eliminate compilation warnings:

Step 1: Align Hardware Addresses and Process Image in HW Config

Open HW Config for the old CPU station (or reference the engineering backup).
Note the exact start addresses of all central and distributed I/O modules (e.g., DI16 x DC24V at address 0...1, AI8 x 12Bit at address 512...527).
Open HW Config for the new CPU (CPU 416-2DP / 410-5H).
Verify that all fieldbus modules (ET 200M, ET 200SP) match the exact PROFIBUS addresses and hardware slot layout.
Manually configure the I/O addresses to match the original layout.
Verify Process Image Partitions: ensure I/O modules processed in OB35 are assigned to the identical Process Image Partition (PIP1 / TPA1).
Save and compile HW Config.

Step 2: Synchronize the Symbol Table

In SIMATIC Manager, navigate to the S7 Program folder of the previous CPU.
Select the Symbols table, right-click, and select Copy.
Paste the Symbol Table into the S7 Program folder of the new CPU, overwriting any blank table.
Open the Symbol Table: confirm that all tag names, absolute addresses, and data types are populated.

Step 3: Close Textual Interconnections in CFC

Open any CFC chart in the new S7 program.
Select Options -> Close Textual Interconnections.
The CFC editor scans the entire chart folder, comparing open textual strings against the newly restored Symbol Table and hardware addresses.
A progress dialog reports: X textual interconnections closed.
Open the Log: verify that all previous yellow textual links have successfully converted into solid green hardware signal connections.

Step 4: Recompile Module Drivers and Charts

Select Chart -> Compile -> Charts as Program.
Ensure the checkbox Generate module drivers is checked.
Select Changes Only (or Entire Scope for initial commissioning).
Confirm compilation finishes with 0 Errors and 0 Warnings.
Download changes to the AS CPU in RUN mode (or download full station during maintenance).

Verification

To confirm that all signals are operational online:
- Switch CFC to online Test Mode (Debug -> Test Mode).
- Open the motor and valve charts that previously exhibited offline symptoms: verify that driver blocks (Pcs7DiIn, Pcs7AnIn) display live dynamic values and signal status 16#80 (Good).
- Open SIMATIC Manager -> PLC -> Diagnostic Buffer: confirm zero I/O access errors (Event ID 16#2942 / 16#2943: I/O access error).
- Open WinCC Runtime: confirm that motor faceplates respond to field commands and feedback signals update without yellow caution banners.

Limitations and Operational Precautions

Cross-AS Links Cannot Be Closed as Textual: If an open textual link points to a block in a different Automation System (cross-AS communication), it cannot be closed using "Close Textual Interconnections". Cross-AS communication requires standard S7 connections configured via NetPro using blocks like BSEND/BRCV or SFB14/SFB15.
Case Sensitivity: Textual interconnections are sensitive to exact spelling and path syntax. A typographical difference (e.g., Pump_101 vs PUMP_101) will prevent the link from closing.
Deleted Symbols Will Revert: If you execute "Close Textual Interconnections" while symbols are still missing, the editor will leave the links open. Do not attempt to force compilation until symbols are verified.

Engineer FAQ

What happens if I download a program with open textual interconnections?

The CPU will compile and download successfully (textual interconnections generate warnings, not fatal compiler errors), but the disconnected block inputs will never receive field data. Motors will fail to start or remain stuck in interlock states because feedback inputs read zero.

Why did some blocks go online while others remained offline?

Blocks connected to valid internal chart logic go online normally. Blocks whose channel drivers were disconnected due to textual interconnections may fail to execute driver routines or display static default values in test mode.

Can I delete a textual interconnection directly in CFC?

Yes. Right-click the yellow textual connection box on the chart margin and select Delete Interconnection. The input parameter reverts to an unconnected state.

How do I know if an address requires a Process Image Partition?

In PCS 7, any block running in a cyclic interrupt organization block (such as OB35, 100 ms) must read its I/O through a Process Image Partition updated synchronously with that OB. If the module is left in the default Process Image (OB1), channel drivers report bad signal status (16#00 or 16#60).

Technical References

Siemens Industry Online Support: SIMATIC PCS 7 CFC for S7 Manual (A5E00278782).
SIOS Entry 109742323: PCS 7 Compendium Part A - Configuration Guidelines (Section: Hardware and Driver Engineering).
SIOS Entry 109809264: SIMATIC Process Control System PCS 7 Advanced Process Library Manual.
Siemens Support FAQ: How to Replace a CPU 41x with a Newer Generation Controller in PCS 7.

Related Tags

CFC
Textual Interconnections
CPU Migration
Hardware Configuration
Channel Drivers
Symbol Table
Industrial Automation

How to Resolve Textual Interconnection Warnings After Replacing a CPU in PCS 7