Understanding Textual References, Block Variables, and Global Data References in PCS 7 CFC and CMT

In SIMATIC PCS 7 CFC and Control Module Type (CMT) engineering, interconnections are categorized into three distinct technical types: Textual References, Block Variables, and Global Data References. Textual References are symbolic string placeholders used to bridge open interconnections across charts or technological units before target instances exist. Block Variables represent localized I/O signal parameters assigned to technological roles within a CMT hierarchy. Global Data References connect block I/Os directly to absolute or symbolic operands defined in the S7 Symbol Table, such as process inputs (PEW), outputs (PAW), bit memories (M), or global shared Data Blocks (DB).

Interconnection Paradigms in SIMATIC PCS 7 CFC and CMT Engineering

Continuous Function Chart (CFC) engineering in SIMATIC PCS 7 relies on dynamic interconnection models that connect block inputs, outputs, and technological parameters across charts, controllers, and field interfaces. With the introduction of modern Control Module Types (CMT) and Equipment Module Types (EMT) in the PCS 7 Master Data Library, engineers must clearly differentiate three fundamental types of references: Textual References, Block Variables, and Global Data References.

Each reference type serves a specific architectural role during plant modularization, standardization, and type-instance synchronization. Conflating these concepts leads to unresolved references during compilation, synchronization overwrites, or broken inter-chart links.

Textual References: Purpose, Syntax, and Lifecycle Management

A Textual Reference (Textuelle Verschaltung) is an open, string-based placeholder interconnection. It allows an engineer to define a connection to a target chart block parameter that does not yet exist offline, resides in a separate chart folder, or will be created dynamically during instance generation.

Key characteristics of Textual References:
- Visual Indicator: In CFC, a textual reference is displayed in the margin with a yellow text marker and warning triangle.
- Syntax: The string follows the format ChartName\BlockName.Parameter (e.g., Plant_Area_1\Motor_01\MotL.FbkRunOut).
- Resolution Mechanism: Textual references are resolved manually via Options -> Manage Textual Interconnections or automatically during full chart compilation. Once the target chart and block are instantiated, PCS 7 converts the text string into a real binary block interconnection.
- Modular Template Decoupling: In CMT engineering, textual references permit library templates to define dependencies (e.g., interlocks from an upstream pump) without requiring the upstream pump to exist in the library.

Block Variables: Technological Role Mapping Within Control Module Types

A Block Variable (Blockvariable / Technological Parameter) is an internal block parameter or interface signal defined within the scope of a Control Module Type (CMT) or Equipment Module Type (EMT). Rather than treating block inputs and outputs as raw software addresses, CMT architecture elevates them to technological elements (Parameters, Signals, Messages) assigned to specific functional roles.

Key characteristics of Block Variables:
- Technological Abstraction: Inside the CMT editor, an engineer maps block parameters—such as VlvL.OpenAut, VlvL.CloseAut, or VlvL.SafePos—as technological 'Block Variables'.
- Internal Chart Interconnections: Block variables define deterministic interconnections between blocks that exist within the same CMT (e.g., wiring the output of an Intlk02 interlock block directly to the Permit input of a MotL motor block).
- Protected Inheritance: During Master Data Library synchronization, internal block variable interconnections are strictly protected. PCS 7 ensures that changes made to block algorithms in the library propagate to all instances without severing local instance bindings.

Global Data References: Interfacing Physical I/O and Symbolic Operands

A Global Data Reference (Globale Operanden / Symbole) connects a block input or output directly to an entity defined in the S7 Symbol Table or a global shared Data Block (DB):

Process Image Inputs and Outputs: Peripheral I/O addresses such as %IW120 (PEW120) or %QW124 (PAW124) mapped to field transmitter signals and valve solenoid drives.
Bit Memory (Flags): S7 memory bits (%M0.0 to %M255.7) used for global controller status flags or legacy communication handshakes.
Shared Data Blocks: Global DB parameters (DB100.DBD0) accessed across legacy S7 programs.

In CMT engineering, physical field I/O connections are configured as Signals. When instantiating a CMT, the engineer assigns the physical symbol (e.g., PT_101_PV) to the CMT Signal attribute in the Process Object View, and PCS 7 automatically establishes the global data reference.

Comparative Architecture Matrix: Interconnection Types in PCS 7

The following matrix summarizes the technical boundaries, storage mechanisms, and behaviors of the three reference types:

Technical DimensionTextual Reference (Textuelle Verschaltung)Block Variable (Blockvariable)Global Data Reference (Globale Operanden)Underlying RepresentationString pointer (Chart\Block.Pin)Instance block I/O parameterSymbol Table address (%IW, %QW, %M, DB)CFC Margin DisplayYellow marker with warning triangleBlue/black chart interconnectionYellow margin box with absolute/symbolic addressPrimary Engineering ScopeCross-chart & inter-unit relationshipsInternal CMT logic & technological rolesField I/O wiring & hardware mappingCMT Synchronization BehaviorResolved to real link when target existsPreserved and enforced by Master Data LibraryPreserved per instance; mapped via SignalsCompiler TreatmentMust be resolved before compile or errors loggedVerified as valid block interface connectionVerified against HW Config & Symbol TableTypical ApplicationUpstream interlock signal across areasWiring Intlk04.Out to VlvL.ProtectWiring transmitter channel %IW256 to Pcs7AnIn.PV_In

Synchronization Behavior Between Master Data Library and Instances

When synchronizing Control Module Types from the Master Data Library to target AS projects (Options -> Match Type and Instances):

Block Variables: Any additions, deletions, or internal rewiring of block variables in the Master Data Library are rigidly pushed to all instances. Instance-specific values (such as alarm setpoints or tuning gains marked with the S7_m_c attribute) are preserved if configured as instance-modifiable.
Global Data References (Signals): Synchronization verifies that the signal definitions match the template structure, but leaves the unique symbolic hardware addresses assigned to individual instances intact.
Textual References: If a template contains a textual reference, it is instantiated as an open reference. Running Options -> Manage Textual Interconnections in the target project reconciles and closes the references against real charts present in the plant hierarchy.

Verification

Verify correct interconnection behavior and reference resolution using the following checks:

In SIMATIC Manager, execute Options -> Charts -> Manage Textual Interconnections. Confirm that all textual references show status 'Closed' or have valid target paths.
In Process Object View, select the Signals tab and verify that every analog/digital I/O signal displays a valid hardware symbol name without red question marks.
Perform a test compilation of CFC charts (Charts -> Compile -> Changes Only). Verify that the compiler log reports 0 errors and 0 warnings regarding open or unresolved interconnections.
Open an instantiated CFC in test mode and confirm that signal values from physical I/O reflect accurately on block inputs.

Limitations and Operational Precautions

Adhere to the following engineering precautions:

Unresolved Textual References: Never download an AS program containing unresolved textual references intended for safety or interlock logic; an open textual reference evaluates to default block values (often zero/false), which could disable protective shutdowns.
Master Data Library Cleanliness: Do not embed absolute hardware addresses or global bit memories directly into Master Data Library CMT templates; always abstract them through CMT Signal interfaces.
Multiproject Cross-References: Textual references that span across different AS projects within a multiproject cannot be resolved by standard CFC compilation; they require AS-OS cross-communication or S7 connection blocks (BSEND/BRCV).

Engineer FAQ

Can an open textual reference prevent an AS program from compiling?

In PCS 7 CFC compilation settings, you can configure whether open textual references trigger a warning or an error. However, best engineering practice mandates resolving all textual interconnections before final commissioning. An unresolved textual reference leaves the block input at its default initialized parameter value, potentially compromising automation sequencing.

What is the difference between a 'Signal' and a 'Parameter' in CMT engineering?

In Control Module Types, a Signal is a technological interface dedicated to field hardware I/O (e.g. process inputs, outputs, or HART variables defined in the Symbol Table). A Parameter is an internal operational value or setpoint (e.g., gain Gain, reset time TI, or limit SP) that can be adjusted by engineers or operators but does not map directly to field bus I/O.

How do I resolve all textual references across a multiproject at once?

In SIMATIC Manager, right-click the project or Charts folder and select Options -> Charts -> Manage Textual Interconnections. In the dialog, click Make Interconnections. PCS 7 parses the entire chart tree and converts all matching textual strings into hard block interconnections.