Resolving Sinamics F01910 Profibus Setpoint Timeout Fault

1. Overview of the Sinamics F01910 PROFIBUS Setpoint Timeout

Fault F01910 "PROFIBUS: Setpoint timeout" is declared by the Sinamics Communication Unit (CU) when the cyclic process-data channel on PROFIBUS DP stops delivering a fresh setpoint telegram from the DP master within the monitoring window enforced by the drive firmware. The detection is performed in two layers: the PROFIdrive stack inside the Control Unit compares the cycle counter of the incoming PZD against the configured bus cycle time, and the application layer compares the setpoint against parameter p2047 "PROFIBUS additional monitoring time".

When F01910 is latched, the drive executes the OFF response mapped in p2100/p2101 (typically OFF3 on a process-critical line, OFF1 on a less critical section), removes pulse enable, and clears bit r899.0 "Control Unit ready". Even after the bus is restored and the controller has returned to RUN, the drive will not re-enable pulses until the fault is explicitly acknowledged and a fresh OFF1 -> ON command (rising edge on STW.0 with STW.1 held high) is issued. In safety-instrumented plants, the F01910 event is mirrored by the F-host PLC as a station failure on the DP slave, which can trip the higher-level Safety Instrumented Function (SIF) and force the production line into a safe state.

The fault value delivered with the alarm in r949 is structured as 0xVVVV_IIII where IIII is the PROFIdrive channel index and VVVV holds the failing PZD word. The most common value 0x0000 0000 indicates a plain cyclic data loss with no specific PZD flagged; a non-zero low word identifies the PZD slot that stopped updating, which is the first place to look when diagnosing intermittent timeouts.

2. Affected Hardware, Control Unit and Firmware Variants

F01910 is generated on every Sinamics platform that exposes a PROFIBUS slave interface through the firmware PROFIdrive stack. The combinations most frequently seen in operating plants are:

The 9-pin Sub-D PROFIBUS connector on every variant above carries the same PROFIdrive V4.2 stack, so a fix engineered on a CU320-2 DP applies to a GM150 with CBC10 without code changes. Always check the FW version in r0018 or via the SINAMICS web server before you tune p2047; firmware < V4.3 treats p2047 in 10 ms steps, while firmware ≥ V4.5 uses 1 ms steps.

3. PROFIBUS DP Architecture, Cycle Time and Telegram 110 Layout

The classic topology for an F01910 case is a SIMATIC S7-400 (CPU 416-3 PN/DP) with an IF-964-DP master module or the integrated DP interface of the CPU. The CPU polls each slave in a fixed token-passing sequence with the DP cycle time T_DP defined in HW Config (or TIA Portal) under "DP master system -> Properties -> Bus parameters". A typical three-node configuration at 1.5 Mbps with 32 bytes I/O per slave resolves to T_DP = 6 ms to 12 ms.

When the DP master is configured with Telegram 110, the PZD layout is fixed by the PROFIdrive profile version 4.2 and is identical for the receive and send directions:

The single most important bit for the F01910 question is STW1 bit 10 "Control from PLC" (German: Steuerung durch SPS). When the DP master drops this bit to 0, the drive firmware interprets the loss of the bit as "controller no longer in charge" and pre-emptively flags the setpoint as invalid. If the loss persists beyond the watchdog window, the drive declares F01910. The control word bit 10 must therefore be held at 1 (TRUE) at all times in the PLC output image of the drive; toggling it during a sequence of motion blocks is a common cause of intermittent F01910 trips.

4. Watchdog Timing Mathematics for the F01910 Budget

Two time-outs are evaluated by the drive:

• Layer A – Bus-level watchdog (r2053[0]): the PROFIdrive stack itself declares a setpoint timeout if a fresh global control bit (GC) or new PZD is not received within 2 × T_DP. This value is not user-tunable, but it bounds the upper end of the monitoring window.
• Layer B – Application watchdog (parameter p2047): the user-configurable additional monitoring time is added on top of the bus-level default. The effective time-out is:

T_F01910 = 2 · T_DP + p2047

For a bus cycle time of T_DP = 10 ms (typical 3-node, 1.5 Mbps segment), the time-out becomes:

• p2047 = 0 ms (default) → T_F01910 ≈ 20 ms
• p2047 = 100 ms → T_F01910 ≈ 120 ms
• p2047 = 500 ms → T_F01910 ≈ 520 ms

Any PLC scan that exceeds T_F01910 (OB1 cycle > 20 ms on a CPU 314 with 8 motion drives, for example) will trip the drive even though the bus is healthy. The recommended engineering rule is:

p2047 = max(3 · t_OB1_max, 100 ms) is a robust starting point for a CPU 416-3 with 3 to 5 drives on one segment. On heavily loaded CPUs where OB1 can stretch to 30 ms, set p2047 to 100 – 200 ms. On thin segments with 1 drive, p2047 = 50 ms is usually sufficient.

5. Root Cause Matrix for F01910

The root cause of F01910 falls into one of four classes. Use this matrix to triage a new event before changing hardware:

6. Step-by-Step Diagnostic Procedure

1. Capture the F01910 context. Open STARTER (or Startdrive in TIA Portal V14+) and read r2125 "Fault buffer", r2124 "Fault value", and r2131 "Fault time received". Note the PLC-side S7 diagnostic buffer entries at the matching wall-clock time. Look for "Station failure", "DP slave not reachable", or "OB not loaded".
2. Read the active telegram configuration. In STARTER, navigate to Communication → PROFIBUS → Telegram configuration. Confirm r0922 "IF1 PROFIdrive PZD telegram selection" matches the value configured in HW Config (typically 110 for a CU320 in vector control). Mismatch causes the drive to interpret incoming PZDs as zero, and within a few cycles the PROFIdrive stack raises F01910.
3. Check the PLC program for the control word bit. Open the DB that holds the drive's output PZD. Confirm bit 10 of the first word (STW1) is held TRUE in every state of the drive sequencer. A common bug is to clear STW1 at the end of a recipe and not re-set it before the next setpoint write.
4. Measure OB1 scan time. Add an FB that records the cycle time into a retentive DB (e.g. R_TRIG and SFC64 "TIME_TCK"). If the maximum scan time exceeds 2 · T_DP, the drive will see a gap in the cyclic frames that the bus layer watchdog treats as a setpoint timeout.
5. Inspect the physical layer. Power down the segment, disconnect every connector, and measure A-B resistance from the master end. The reading must be ≈ 220 Ω with one terminator or ≈ 110 Ω with both terminators. Any other value indicates a short, an open line, or an extra terminator. Re-tin the D-sub pins if the segment was commissioned in 2008 or earlier.
6. Capture a Profibus trace. Use a Profibus monitor (e.g. Amprolyzer, Softing PB-T3, Inatra PROFI-line) or the integrated Profibus diagnostics of the CPU 416-3 (diagnose -> Profibus -> statistics) to log the bus statistics. Watch for retry count, slave diag frames, and the cyclic-frame jitter. A cyclic-frame jitter of more than 30 % of T_DP indicates an EMC or bandwidth issue.
7. Test the controller in isolation. Disconnect the drive, set a constant cyclic write of a "safe word" into the drive's output PZD with STW1.10 = 1, and observe whether the drive drops the connection. If it stays connected for 24 hours, the issue is in the controller program; if it drops, the issue is physical or firmware.
8. Review the backup PLC swap history. When the user reported that "changing the PLC" appeared to clear the fault for a few minutes, this is a tell-tale sign of a marginal PB cable, a marginal DP connector, or a missing OB82 / OB86 on the new PLC. The PLC did not "fix" the bus; it just changed the reflection / capacitance enough to postpone the next drop-out.

7. Tuning p2047 and the Surrounding PROFIdrive Parameters

The headline change for F01910 is to set p2047 from 0 to a value that absorbs the worst-case OB1 jitter plus the bus-cycle jitter. As a rule of thumb:

• p2047 = 100 ms – safe for a CPU 416-3 with up to 8 drives, 1.5 Mbps, OB1 ≤ 25 ms.
• p2047 = 200 ms – safe for a CPU 314-2DP with 3 drives, 1.5 Mbps, OB1 ≤ 50 ms.
• p2047 = 500 ms – safe for a CPU 315-2DP with 2 drives, 45.45 kbps, very long cables.

8. PLC Program Hygiene – OB82 / OB86, Control Word Bit 10 and SFC14 / SFC15

A CPU that runs without OB82 (diagnostic interrupt) and OB86 (rack failure) will deliver stale PZDs to the drives on a bus glitch and the drives will time out. The minimum program structure on the PLC side is:

• OB1 (free cycle) – runs every scan, calls the drive sequencer FB and writes the output PZDs.
• OB82 (diagnostic interrupt) – logs the slave diagnostic to a ring buffer DB and clears the diagnostic.
• OB86 (rack failure / DP station failure) – sets a "drive not available" flag and raises a controlled stop request.
• OB122 (I/O access error) – logs the failing PZD address and forces a controlled stop on the affected drive.

The SFC14 "DPRD_DAT" and SFC15 "DPWR_DAT" blocks must be called every cycle and their RET_VAL/STATUS must be checked. A typical pattern in Structured Text (works in both Step 7 V5.7 and TIA Portal V18) is:

// ST sample for reading 12 bytes of actual values from drive 1 (input area PE 256..267)
#status_rd := DPRD_DAT(LADDR := 256, RET_VAL := #ret_rd, RECORD := #zsw_struct);
IF #ret_rd <> 0 THEN
    // DP error – log, ramp master command to 0, raise a soft stop
    #stw1_struct.stw1.steuerwort_bits.control_from_plc := FALSE;
    #stw1_struct.stw1.steuerwort_bits.off1            := TRUE;  // OFF1
    #stw1_struct.stw1.steuerwort_bits.on_off2         := FALSE;
    #stw1_struct.stw1.steuerwort_bits.on_off3         := FALSE;
END_IF;

// Always set bit 10 = "control from PLC" to 1 to avoid F01910
g_bt10 := TRUE;
#stw1_struct.stw1.steuerwort_bits.control_from_plc := g_bt10;

// Write 12 bytes of setpoints to drive 1 (output area PA 256..267)
#status_wr := DPWR_DAT(LADDR := 256, RECORD := #stw1_struct, RET_VAL := #ret_wr);
IF #ret_wr <> 0 THEN
    // DP error – alarm, do not retry blindly, hand over to backup PLC
    "db_alarm".drive1_dp_error := TRUE;
END_IF;

For the SystemInterruptTask that the user mentioned: a "blank" OB40 / OB82 / OB86 means the CPU does not crash on the bus interrupt, but it also does not log the event. Replace the blank blocks with a minimal logging FB so that future F01910 events are not lost in the PLC diagnostic buffer.

9. Field Commissioning Procedure for a Stable PROFIBUS Segment

1. Use a Siemens 6XV1830-0EH10 (or higher) Profibus cable, with the characteristic impedance of 150 Ω and a loop resistance of ≤ 110 Ω/km. Do not mix cable batches on a single segment.
2. Place the bus terminator ON only at the two physical end nodes. On a three-node segment, this is the master (CPU 416-3) and the last drive. All intermediate nodes must have the terminator OFF.
3. Ground the cable shield at the cabinet entry plate, using a 360° EMC gland. A "pig-tail" shield ground adds 30 – 50 nH of inductance and converts HF noise into common-mode voltage that corrupts the differential Profibus signal.
4. Separate the Profibus trunk from the VFD output cable by at least 200 mm. If they must cross, cross at 90°. Never run the Profibus cable in the same conduit as the motor cable.
5. Set the bus address on every drive with the rotary switch (or p0918). Document the address in the HW Config and in STARTER. Address clash is a silent F01910 trigger because the master talks to the wrong slave and the addressed slave times out.
6. Set p0922 = 110 on every drive. Restart the drive (power cycle) to commit the change.
7. In HW Config, set the bus profile to "Standard" and the bus cycle to the lowest value the segment can support (typically 6 ms for 1.5 Mbps). Verify the value in STARTER > Drive unit > Communication.
8. Set p2047 = 100 (or 200 / 500 per the matrix above). Save the parameter set with "Copy RAM to ROM" and then perform a warm restart of the drive.
9. Run the segment for 24 h with the controller in RUN and a constant non-zero setpoint. Verify that r829[0..2] "Message counter" and r833[0..2] "Clock counter" are incrementing on every drive.
10. Force a bus glitch (pull the Profibus connector for 200 ms) and confirm that the drive drops out, declares F01910, and recovers within 2 s of the bus being restored and the fault being acknowledged.

10. Verification Matrix and Related Fault Codes

Use the following matrix to confirm the fix and to distinguish F01910 from related faults that can mask it:

Verification procedure for a closed F01910 case:

1. Drive is in "Ready to switch on" (ZSW1.0 = 1) with PLC in RUN.
2. STW1.10 = 1 in the PLC output PZD at all times. Capture a Profibus trace to confirm.
3. r2125 shows no F01910 in the last 72 h.
4. r829[0] increments every T_DP ms.
5. r978 "Slave sign of life" shows no dropouts over 24 h.

11. Frequently Asked Questions