Mastering the WinCC Extended Status Display - Bit Number Mapping, Graphic Index Binding, and 4-Status-Word Combinatorics

In SIMATIC WinCC (PCS 7 Classic and APL), the Extended Status Display (ESD) is a high-performance graphical object that decodes up to four 32-bit status words from the controller into discrete runtime visual states. In the ESD Configuration Dialog, 'BIT NUM' specifies the exact bit positions (0 to 31) evaluated within each active status word. Under the 'Assign Pictures' tab, the object automatically generates $2^k$ binary state indexes (where $k$ is the total count of evaluated bits across all enabled status words), mapping each unique combination of 0s and 1s to a specific graphic file (.emf or .bmp) from the project GraCS folder.

Functional Architecture of the Extended Status Display

The Extended Status Display is the foundational visual building block for animated multi-state equipment representations (valves, motors, pumps, circuit breakers, and dampers) across SIMATIC PCS 7. Unlike standard status displays that monitor a single analog or integer variable:
- Direct Bitmask Evaluation: The ESD evaluates raw binary status words (DWORD) directly from automation blocks without requiring PLC programmers to pack integer state codes or HMI engineers to execute VBScript bit-shifting routines.
- Input Channels: The ESD provides four dedicated input channels: Status1, Status2, Status3, and Status4.
- Index Generation Engine: The object reads the bit states configured under each channel, constructs a composite binary word, and converts that word into a base-10 numerical index pointing to an image in the project GraCS library.

Demystifying 'BIT NUM' and Truth-Table Index Generation

In the ESD Configuration Dialog:
1. The Purpose of 'BIT NUM':
- A standard PLC DWORD contains 32 individual bits (numbered 0 to 31).
- In most automation blocks (like APL MotL or VlvL), physical states occupy specific bit positions (e.g. Bit 20 = Stopped, Bit 23 = Running).
- In the ESD dialog, selecting from status word 1 and checking a specific BIT NUM instructs the object: 'Only evaluate this specific bit from the connected DWORD'.

Single-Bit Evaluation ($2^1 = 2$ States):
- If you configure Status Word 1 $\rightarrow$ Bit 23 (Motor Running):
- When Bit 23 is 0 $\rightarrow$ Index 0 is active $\rightarrow$ Display motor_stopped.emf.
- When Bit 23 is 1 $\rightarrow$ Index 1 is active $\rightarrow$ Display motor_running.emf.
Two-Bit Evaluation ($2^2 = 4$ States):
- If you configure Status Word 1 $\rightarrow$ Bit 20 (Stopped) AND Bit 23 (Running):
- Index 0 (00): Neither active $\rightarrow$ Display motor_transition.emf.
- Index 1 (01): Bit 20=1, Bit 23=0 $\rightarrow$ Display motor_stopped.emf.
- Index 2 (10): Bit 20=0, Bit 23=1 $\rightarrow$ Display motor_running.emf.
- Index 3 (11): Bit 20=1, Bit 23=1 $\rightarrow$ Display motor_fault.emf (sensor contradiction).

Multi-Status-Word Combinatorics and Graphic Assignment

The true power of the ESD lies in evaluating multiple status words simultaneously:

Combining Actuator State with Operational Mode:
- Status Word 1 connected to MotL.Status2 (Actuator Feedback):
- Select Bit 23 (Running).
- Status Word 2 connected to MotL.Status1 (Operational Mode):
- Select Bit 0 (Automatic Mode active).
- This 2-bit combination produces 4 distinct operating states:
- Index 0 (Bit23=0, Bit0=0): Manual Mode, Motor Stopped.
- Index 1 (Bit23=1, Bit0=0): Manual Mode, Motor Running.
- Index 2 (Bit23=0, Bit0=1): Automatic Mode, Motor Stopped.
- Index 3 (Bit23=1, Bit0=1): Automatic Mode, Motor Running.
Assigning Pictures in the Configuration Tab:
- Navigate to the Assign Pictures tab.
- The grid lists every generated index from Index 0 to Index (2^k - 1).
- Double-click each index row or use the Assign Picture browser to select the desired .emf or .bmp graphic from the GraCS library.
- For unused or abnormal bit combinations (such as Index 3 where both stopped and running are high), always assign a conspicuous fault graphic (apl_bi_MotL_err.emf).

Extended Status Display Truth Table and Index Mapping Example

The following table details a 3-bit multi-status-word configuration evaluating equipment status and fault:

State IndexStatus Word 1 (Bit 20: Stopped)Status Word 1 (Bit 23: Running)Status Word 2 (Bit 5: Tripped)Equipment Operating StateRecommended Graphic FileIndex 0000Transition / Unpoweredpump_trans.emfIndex 1100Stopped (Normal)pump_off.emfIndex 2010Running (Normal)pump_on.emfIndex 3110Sensor Contradiction / Faultpump_err.emfIndex 4001Tripped (Idle)pump_trip.emfIndex 5101Tripped while Stoppedpump_trip.emfIndex 6011Overload Running / Alarmpump_alarm.emfIndex 7111Severe Hardware Contradictionpump_err.emf

Verification

To confirm that the Extended Status Display animates accurately across all operating modes:
1. Open the WinCC process screen containing the configured ESD object in Graphics Designer.
2. In the ESD properties, verify that each Status tag is correctly bound to the corresponding CFC structure tag (e.g. Motor1/Status2).
3. Launch WinCC Runtime.
4. Using CFC test mode or PLCSIM, sequentially manipulate the target bits:
- Force Bit 20 = 1: Confirm the screen displays the stopped graphic.
- Force Bit 23 = 1: Confirm the screen updates immediately to the running graphic.
- Force both bits = 1: Confirm the screen renders the fault graphic.
5. Verify that graphic transitions execute instantaneously with zero flickering or script execution lag.

Limitations and Operational Precautions

When engineering with the WinCC Extended Status Display:
1. Exponential Index Expansion: Never select more than 6 to 8 total bits. Selecting 8 bits generates $2^8 = 256$ separate graphic indexes; selecting 10 bits generates 1024 indexes, creating excessive memory overhead and making graphic management unmanageable.
2. Missing Picture Fallback: If an active runtime index is not assigned a graphic in the configuration table, the ESD renders as completely blank / invisible, which can confuse operators into believing the equipment was deleted. Always populate all generated indexes.
3. Use Group Value Caution: Enabling 'Use group value for display' multiplies the total index count by the alarm status states (Unacknowledged, Acknowledged). Ensure you understand the expanded index table before enabling this feature.

Engineer FAQ

What happens if a bit configured in BIT NUM is outside the 0 to 31 range?

The configuration dialog will reject entries outside 0 to 31 because standard S7 DWORD data types contain exactly 32 bits.

Can the Extended Status Display read floating-point REAL values?

No. The ESD evaluates binary bits within DWORD structures exclusively. To animate analog thresholds (e.g. Low, High, HighHigh), use the Extended Analog Status Display or WinCC Bar Graph object.

Why does my ESD show Index 0 when the motor is running?

This happens if the wrong status word is connected to the ESD input tag, or if the bit number specified does not match the block's internal bit assignment. Check the APL library manual to confirm the exact bit position for 'Running' (e.g. Bit 23 in Status2 for MotL).

Can I use animated GIFs in the Extended Status Display?

WinCC Extended Status Displays support static EMF, BMP, and WMF formats natively. Animated GIFs are not recommended as they can cause GDI resource leaks; multi-frame animation in PCS 7 is implemented using flashing bit properties or cyclically toggling indexes.