Resolving CFC Interconnection Error 1739:60451 in SIMATIC PCS 7

SIMATIC PCS 7 CFC Error 1739:60451 ('Wrong signal or no signal available') occurs when attempting to interconnect a block input or output pin (such as PV_In on an analog channel driver) to a hardware peripheral address (IW, QW, PIW) that lacks a typed symbolic entry in the project Symbol Table, has an uncompiled hardware configuration, or presents a data type mismatch. Resolving this error requires defining the peripheral address as a typed symbol (e.g., WORD) in the Symbol Table, compiling HW Config, and establishing the connection using the symbolic operand picker.

Root Causes of Signal Interconnection Error 1739:60451

Continuous Function Chart (CFC) in SIMATIC PCS 7 enforces strict symbolic addressing and type safety for all hardware I/O interconnections. When an engineer copies an existing chart or channel driver block (e.g., Pcs7AnIn or CH_AI) and attempts to manually overwrite or connect an input pin such as PV_In to an absolute peripheral address like IW 196 or PIW 196, the CFC editor rejects the input with error 1739:60451.

The underlying causes include:
1. Missing Symbol Table Entry: PCS 7 requires all field I/O connected to driver blocks to possess a defined symbolic name in the S7 Program Symbol Table. Absolute peripheral addresses entered as plain text are rejected.
2. Data Type Mismatch: The block pin expects a specific data type (e.g., WORD for raw peripheral inputs on classic drivers, or a structured data type like STRUCT containing value and status). If the symbol is defined as INT, DWORD, or REAL, CFC blocks the interconnection.
3. Hardware Configuration Desynchronization: If new I/O modules were added to HW Config but the configuration was not compiled and saved, the engineering system does not recognize the address as a valid physical channel.
4. Channel Driver Auto-Interconnection Mechanism (Generate Module Drivers): PCS 7 channel drivers are designed to connect to symbolic module tags so that the compiler's Generate Module Drivers task can automatically route diagnostic wires, rack failure monitoring, and quality codes.

Diagnostic and Resolution Procedure for Symbolic I/O Interconnections

Follow this procedure to eliminate error 1739:60451 and establish valid I/O interconnections in CFC.

Prerequisites

SIMATIC Manager open with write access to the target AS project.
The physical hardware address confirmed in HW Config (e.g., analog input module configured at start address 196).

Step 1: Verify Hardware Configuration

In SIMATIC Manager, open HW Config for the target automation station.
Locate the I/O module hosting the signal.
Double-click the module to inspect its properties and verify the assigned input/output address range (e.g., inputs 196...211).
Select Station -> Save and Compile. Do not proceed if HW Config has uncompiled changes.

Step 2: Define the Address in the Symbol Table

In SIMATIC Manager, open the Symbols table located inside the S7 Program folder.
Add a new row for the required I/O channel:
- Symbol: Enter a unique, descriptive tag name (e.g., TT_101_Raw).
- Address: Enter the physical address (e.g., IW 196 or PIW 196).
- Data type: Specify WORD (standard raw peripheral input type for analog driver blocks like Pcs7AnIn or CH_AI).
- Comment: Add functional plant description (e.g., Reactor Bed Temperature Raw Value).
Click Save (Ctrl+S) and close the Symbol Table.

Step 3: Establish the Connection in CFC

Open the CFC chart containing the channel block.
Select the input parameter pin (e.g., PV_In).
Press Insert -> Interconnection to Address... or press shortcut key F3 (or right-click the pin and select Interconnection to Address / Operand).
In the operand dialog, do not type absolute text IW 196. Instead:
- Select the Symbolic tab or browse the symbol list.
- Select the newly created symbol TT_101_Raw.
Click OK. The connection establishes cleanly, displaying the symbolic name and absolute address on the chart margin.

Verification

Inspect the CFC chart margin. The connected pin must display the green symbolic name along with the absolute address in parentheses (e.g., TT_101_Raw (IW 196)).
Select Chart -> Check Consistency -> Entire Program and confirm that zero interconnection errors are reported.
Select Chart -> Compile -> Changes Only with Generate module drivers enabled. Confirm that compilation succeeds and that the compiler automatically instantiates diagnostic blocks (MOD_D1, RACK) and interconnects quality code parameters without error.

Limitations and Operational Precautions

Peripheral addresses outside the cyclic process image partition must be addressed as PIW in classic STEP 7, but in PCS 7, configuring the process image partition in HW Config allows standard IW addressing.
Never attempt to type raw numbers into the input field of a channel driver in CFC; CFC treats raw numeric entries as literal constant values rather than hardware I/O addresses, triggering type mismatch errors.
Modern APL drivers (such as Pcs7AnIn) use structured inputs containing value and status in certain operating modes. Ensure you connect peripheral hardware to the appropriate raw input pin.

Engineer FAQ

Why can't I just type 'IW 196' directly onto the block pin?
CFC interprets direct text entry into an input field as a numerical constant or variable name rather than a hardware address. To connect to physical hardware, you must use the Interconnection to Address dialog (F3) or enter a recognized symbolic name.
What data type should I use in the Symbol Table for digital inputs?
For digital inputs connecting to Pcs7DiIn or CH_DI, use data type BOOL in the Symbol Table (e.g., I 12.0 assigned to BOOL).
Why does 'Generate module drivers' fail after fixing the error?
If 'Generate module drivers' fails during compilation, check that the hardware module in HW Config has diagnostic interrupts enabled and that the module is assigned to an existing diagnostic structure.
Does resolving this error require a CPU Stop download?
No. Adding a symbol to the Symbol Table and interconnecting it in a CFC chart can be compiled and downloaded using Changes Only in RUN mode, provided the physical I/O module was already compiled into the CPU runtime.
What is the difference between error 1739:60451 and error 1739:60450?
Error 1739:60451 specifically indicates that the entered signal address does not exist or has an incompatible data type for the target pin, whereas 1739:60450 generally denotes an illegal interconnection between incompatible chart blocks or circular references.

Technical References

Siemens Industry Online Support Entry ID 109748805: CFC for SIMATIC S7 / PCS 7 Manual.
Siemens SIMATIC PCS 7 Advanced Process Library (APL) Function Manual: Driver Blocks and Signal Processing.
Siemens Process Automation Guide: Configuring Hardware and Symbols in PCS 7 Engineering.

Resolving CFC Interconnection Error 1739:60451 in SIMATIC PCS 7