SINAMICS S120 PROFIBUS GSD Diagnostic Data: SFC51 Reading Method

Overview

The SINAMICS S120 drive family exposes a defined PROFIBUS DP slave diagnostic interface that can be evaluated from a SIMATIC controller. Engineers commonly attempt to read the drive's diagnostic data with SFC13 (DPPRRM) after parsing the GSD file, but Siemens Product Support has confirmed that this path returns no useful values for SINAMICS drives: SFC13 was designed for distributed I/O stations (ET 200M, ET 200S), not for complex drive objects. The correct technique is to use SFC51 (RDSYSST / Read SSL) with SSL-ID W#16#00B4 on a CP 443-5 extended as a DP master, or to evaluate the raw response telegrams and the diagnostic frame visible inside HW Config of STEP 7 / TIA Portal.

The purpose of this reference is to:

1. Locate the diagnostic data section in the SINAMICS S120 GSD file.
2. Explain the Max_Diag_Data_Len = 244 constraint and how it shapes the receive buffer.
3. Decode the standard, identifier-related, and device-related diagnostic blocks.
4. Implement the recommended SFC51 (RDSYSST) W#16#00B4 alternative.
5. Verify the read-out and map the bytes to SINAMICS fault and alarm words (r0945/r2122).

Prerequisites

• STEP 7 V5.5 or TIA Portal V16+ with the SINAMICS S120 GSD file installed in the hardware catalog.
• SINAMICS S120 Control Unit (CU320-2 DP or CU320-2 PN) with PROFIBUS DP interface active.
• CP 443-5 Extended as DP master (for SFC51 SSL W#16#00B4 path) or an integrated PROFIBUS port on S7-300/400 CPU.
• The matching GSD file revision: SIEM80FA.GSD or later. The diagnostic block layout described below corresponds to GSD revision matching firmware V5.x of the SINAMICS S120.
• Manual reference: SINAMICS S120 Communication Function Manual (1218).

Where to Find the Diagnostic Section in the S120 GSD File

Open the GSD file in any text editor and search for the keyword Diagnosis or the section header ;--- Diagnosis ---. A typical SINAMICS S120 GSD excerpt from the diagnostic block looks like this:

;--- Diagnosis ---
Diagnostic_Alarm_supp      = 1
Extra_Alarm_SAP_supp       = 1
Alarm_Sequence_Mode_Count   = 0
Alarm_Type_Mode_supp        = 1
Max_Diag_Data_Len          = 244

The most important entry is Max_Diag_Data_Len = 244. This value dictates the maximum number of bytes the slave can place in its diagnostic response telegram. When you allocate the receive buffer in the user program, set its length to 244 bytes; anything shorter risks truncation, anything longer is rejected by the SFC. The other flags describe alarm model capabilities:

The GSD does not describe the content of each diagnostic byte - that description is given by the PROFIBUS standard (EN 50170 Volume 2 / IEC 61158-6) and refined by the SINAMICS S120 Communication Function Manual. The GSD only declares the size and the alarm model features.

Why SFC13 (DPPRRM) Fails on SINAMICS S120

SFC13 DPPRRM - "DP read diagnostics of a slave" - expects a PROFIBUS slave with a fixed, contiguous module arrangement (ET 200M with one DI and one DO, for example). Its internal parsing assumes the standard PROFIBUS diagnostic block layout where each module's status is reported in a known bit position of the identifier-related diagnostics. SINAMICS S120, however, is a modular drive object with virtual slots (DO1 = Control Unit, DO2 = first drive axis, DO3 = second drive axis, etc.). The mapping of slot number to drive object is dynamic and is not exposed in the same way as physical I/O modules.

Siemens Product Support response, summarized:

"We have concluded that SFC13 will not deliver useful values in connection with SINAMICS. The SFC13 was meant for distributed IO stations and not drives."

Therefore, do not allocate a buffer of 244 bytes to SFC13 and expect a clean diagnostic payload back. The FB returns either zeros, frozen previous data, or the SFC sets RET_VAL = W#16#80A2 (DP slave failure) when the drive is busy processing a write request.

The Recommended Path: SFC51 (RDSYSST) with SSL_ID W#16#00B4

When the SIMATIC station uses a CP 443-5 Extended as PROFIBUS DP master, the diagnostic data of every configured slave can be read out centrally with SFC51 (RDSYSST) using SSL-ID W#16#00B4 (partial list excerpt of "DP slave diagnostic data"). The SSL part index INDEX corresponds to the configured PROFIBUS address of the S120 drive:

STEP 7 V5.5 Implementation Skeleton (SCL)

FUNCTION_BLOCK FB_DiagS120
VAR
    iRetVal  : INT;            // RET_VAL of SFC51
    wBusy    : BOOL;           // BUSY flag
    abDiag   : ARRAY[0..243] OF BYTE;   // 244-byte buffer
    wIndex   : WORD;           // PROFIBUS address of the S120
END_VAR
BEGIN
    // Call SFC51 - Read SSL
    iRetVal := RDSYSST(
        SZL_ID   := W#16#00B4,    // DP slave diagnostics
        INDEX    := wIndex,        // e.g. W#16#0004 for DP addr. 4
        SZL_HEADER := NULL,        // not used for partial list
        DR       := abDiag,        // 244-byte target buffer
        BUSY     := wBusy
    );

    IF (iRetVal = 0) AND (NOT wBusy) THEN
        // abDiag[0]  = Station status 1
        // abDiag[1]  = Station status 2
        // abDiag[2]  = Station status 3
        // abDiag[3]  = Diag.master addr
        // abDiag[4..5] = Ident number high/low (e.g. 0x80FA)
        // abDiag[6..7] = Header for identifier-related diagnostics
        // abDiag[8..]  = Identifier-related + device-related blocks
    END_IF;
END_FUNCTION_BLOCK

Alternative: Reading Diagnostic Data Online in HW Config

For commissioning, open the S120 slave in HW Config → DP Slave Diagnostics. STEP 7 will show the same 244-byte payload decoded. A typical frame from a multi-axis S120 system resembles:

Standard diagnostics              : 00 0C 00 02 80 1E
Identifier-related diagnostics    : 43 00 00
Device-related diagnostics        : 08 82 00 00 00 00 00 00
Device-related diagnostics        : 08 9F 00 00 00 2A 11 05

Each block can be parsed as follows:

The 0x801E ident number is the PNO-registered ident for the SINAMICS S120 family. If the ident on the wire differs (e.g. 0x80C0 for an older S120 firmware V4.x), the GSD revision does not match the loaded firmware - update the GSD or the CU firmware to make the diagnostic blocks parse correctly.

Decoding Channel and Extended Channel Diagnosis

The device-related diagnostic blocks of the S120 follow PROFIBUS convention:

• Status type 0x82 = channel diagnosis, 8 bytes: 1 byte channel number, 1 byte error code, 2 bytes channel properties, 2 bytes user-defined (often drive fault number r0945 truncated), 2 bytes additional info.
• Status type 0x9F = extended channel diagnosis, 8 bytes: same as 0x82 plus an extra 2 bytes that point to the DO (drive object) and the exact fault code stored in r0945 / r2122.

For the example frame 08 9F 00 00 00 2A 11 05 (with the preceding header):

Step-by-Step: Commissioning the Diagnostic Read-out

1. Install the GSD. In STEP 7 V5.5 choose Options → Install GSD File and point to the latest S120 GSD for your CU firmware. Restart HW Config.
2. Wire the S120. Configure the CU320-2 DP at the correct PROFIBUS address (default 3, change with PROFIBUS address switches on the CU). Match the baud rate (typically 12 Mbit/s for S120).
3. Configure the slots. Insert the standard telegram (e.g. Telegram 1, 2, 3, 4, 5, 6, 7, 9, 102, 103, 105, 106) for each drive axis. The number of slots the GSD exposes determines the maximum identifier-related diagnostic bitfield width.
4. Compile and download the HW Config to the CPU.
5. Insert SFC51 call in OB1 with SSL-ID W#16#00B4 and INDEX = PROFIBUS address of the S120. Allocate a 244-byte ANY pointer to a static DB or instance FB.
6. Monitor the call: RET_VAL should be 0, BUSY should be 0 after one cycle. The first 6 bytes of the buffer contain the standard diagnostic block.
7. Map the SINAMICS fault number from the extended channel diagnosis to a textual message using the S120 List Manual (article number 6SL3097-4AP00-0BPx).

Verification Procedure

1. Force a known drive fault by writing p0009 = 1, p0976 = 1 (factory reset is too drastic - instead use p2100/p2101 to inject a fault).
2. Observe the diagnostic buffer: abDiag[1] bit 3 ("diagnostic data present") must toggle to 1.
3. Confirm abDiag[4..5] still equals 0x801E (or the ident of the actual GSD).
4. Decode the device-related blocks and verify they match the fault number shown on the AOP30 or in r0945[0] of STARTER / Startdrive.
5. Clear the fault from the drive side and verify the diagnostic frame returns to 00 0C 00 02 80 1E.

Troubleshooting Matrix

Related Reading and Standards

The diagnostic structure of the S120 follows the generic PROFIBUS DP slave diagnostic model defined in IEC 61158-6 / EN 50170 Volume 2. For background on the header and the bitfield layout, the GSD specification of PNO (PROFIBUS Nutzerorganisation) is the authoritative source.

For drive-specific decoding, see:

• SINAMICS S120 Communication Function Manual (firmware V5.x) - section on PROFIBUS diagnostic interface and GSD handling.
• Configuring SINAMICS S120 (TIA Portal manual collection) - GSD integration in the S7-1500 hardware catalog.
• SINAMICS S120 List Manual (parameter r0945 fault list and r2122 alarm list).

Field-Notes Summary

• The S120 GSD tells you how much diagnostic data the slave can emit (Max_Diag_Data_Len = 244) and which alarm model features are available, but never what each byte contains.
• SFC13 is the wrong FB. Use SFC51 (RDSYSST) with SSL W#16#00B4 on a CP 443-5 Extended, or read the cyclic status word ZSW1 directly from the process image.
• Always cross-check the decoded fault number with parameter r0945 / r2122 in STARTER or Startdrive - the diagnostic frame is consistent with the cyclic data, not a separate source of truth.
• Reserve 244 bytes in the target buffer to avoid truncation.
• If the ident number on the wire does not match the GSD ident, you have a GSD / firmware mismatch - update the GSD before commissioning the diagnostic application.