Decoding Diagnostic Alarm Placeholders (16#@1%X@) in SIMATIC PCS 7 System Driver Charts

In SIMATIC PCS 7, alarm strings featuring dynamic format placeholders such as 'Failure connection ID: 16#@1%X@' or 'Module 1/4/4: Failure' are automatically generated by the Driver Generator in the '@' system charts to report hardware and communication diagnostics. The token '@1%X@' is a standard C-printf format specifier where '@1' denotes the first associated message value parameter and '%X' formats the data as a hexadecimal integer representing a connection ID, logical subnet, or status code. Messages formatting hardware coordinates as 'Module 1/4/4' represent [Master System]/[Station Address]/[Slot Number]. Engineers can locate the exact failing device by cross-referencing these coordinates directly within HW Config.

Architecture of System Diagnostic Messages in '@' Charts

During Continuous Function Chart (CFC) compilation with the option 'Generate module drivers' enabled, SIMATIC PCS 7 scans the hardware configuration (HW Config) and automatically populates dedicated '@' charts with system driver blocks. These blocks include MOD_* (e.g., MOD_D1, MOD_HA), RACK, SUBNET, OB_BEGIN, and RED_CONNECT.

These diagnostic blocks continuously evaluate CPU System Status Lists (SSL / SZL) and respond to operating system interrupt OBs (OB82 diagnostic alarm, OB83 pull/plug interrupt, OB85 program execution error, OB86 rack failure). When an I/O card loses backplane power, a field bus wire is severed, or a redundant connection loses synchronization, the blocks issue Alarm_8P messages directly to WinCC Alarm Logging with dynamic system attributes.

Deciphering Dynamic Format Specifiers (@1%X@ and Module Coordinates)

To display precise technical data without creating thousands of unique static alarm strings, PCS 7 utilizes standardized dynamic string placeholders embedded in message definitions:

Message Format PatternMeaning of TokenTypical ExampleDecoded Engineering Meaning16#@1%X@Associated value 1 formatted in Hexadecimal16#1001Connection ID or logical hex communication endpoint@1%d@Associated value 1 formatted in Decimal4Decimal rack, channel, or error code numberModule s/r/mSubnet / Rack / Slot coordinateModule 1/4/4: FailureMaster System 1, ET 200M Station Address 4, Slot 4 cardRedundancy loss ID: 16#@1%X@Redundant connection status token16#0ARedundant link loss on S7-REDCONNECT endpoint 10

In redundant networks, a single physical rack failure may trigger multiple diagnostic messages (e.g. 8x connection warnings) because redundant driver instances across both CPU subracks independently log the loss of their respective partner paths.

Step-by-Step Diagnostic Workflow to Pinpoint Hardware Faults

When a cryptic system driver message appears in the WinCC alarm banner, follow this structured diagnostic procedure:

Identify Coordinate Tokens: Examine the alarm text in WinCC AlarmControl. Note the string coordinates, such as Module 1/4/4: Failure or Connection ID: 16#1002.
Cross-Reference in HW Config: Open SIMATIC Manager and launch HW Config for the target AS. Locate Master System 1 (PROFIBUS DP 1 or PROFINET IO-System 100). Browse to Station Address 4 (ET 200M node). Click slot 4 to identify the exact module model (e.g., SM 331 8x12 Bit 6ES7331-7KF02-0AB0).
Open Online Hardware Diagnostics: In HW Config, select PLC -> Open Online. Double-click the faulted module to open Module Information. Inspect the Diagnostic Interrupt tab to view the exact hardware fault (e.g., Wire break on channel 3, Internal auxiliary voltage missing, or Configuration mismatch).
Inspect Connection IDs in NetPro: If the message reports a connection ID (e.g., 16#@1%X@), open NetPro. Locate the connection table for the AS CPU and match the hexadecimal connection ID (e.g., 16#1002) to find the failing partner station or redundant link.
Physical Panel Inspection: Verify LED indicators on the physical rack: SF (System Fault), BF (Bus Fault), and individual red channel LEDs.

Verification

Verify system diagnostic resolution through these technical steps:

Hardware LED State: Inspect the physical module and ET 200 interface header. Confirm that red SF and BF LEDs have extinguished, leaving only green power/active indicators.
Module Diagnostic Buffer: Open PLC -> Module Information -> Diagnostic Interrupt in HW Config Online. Confirm that the buffer reports 'No diagnostic interrupt present' or 'Fault cleared'.
WinCC Alarm Clearing: In WinCC OS Runtime, verify that the diagnostic message transitions to 'Gone' status in the alarm list and can be acknowledged cleanly.

Limitations and Operational Precautions

When handling system driver alarms, adhere to these maintenance and engineering precautions:

Never Edit '@' Charts Manually: The '@' charts are system-managed. Any manual edits, deleted blocks, or modified connections inside charts beginning with '@' will be completely overwritten and destroyed during the next CFC compilation.
Driver Generator Option Consistency: Never compile CFC with 'Generate module drivers' unchecked in a production environment unless explicitly performing a specialized test; doing so disables hardware diagnostic monitoring entirely.
Maintenance Station Integration: For comprehensive visualization of hardware health without manual string decoding, deploy the SIMATIC PCS 7 Maintenance Station (MS), which natively maps these diagnostic codes into intuitive graphical plant views.

Engineer FAQ

Why are there so many redundant connection failure alarms for a single bus glitch?

Redundant architectures (S7-400H / S7-REDCONNECT) monitor multiple physical and logical communication paths. A single transient glitch triggers separate path diagnostic blocks, resulting in multiple localized alarm entries.

Can I suppress system driver messages from reaching the main operator alarm banner?

Yes. System hardware messages belong to the message class 'Control System Fault' (AS-Leittechnik Störung). WinCC AlarmControl filters can route these messages exclusively to dedicated maintenance screens.

What does 'Module 0/0/0' mean in a diagnostic message?

A coordinate of 0/0/0 typically indicates a central rack or power supply diagnostic event directly related to the central CPU chassis rather than a distributed fieldbus slave.