SINAMICS G120 CU240 Hidden Parameters: P0700, P2040 Access Fix

Problem Statement: SINAMICS G120 CU240 BOP Hides Expected Parameters

After running basic commissioning on a SINAMICS G120 with a CU240B-2 (or CU240E-2) Control Unit, engineers attempting to validate or modify the PROFIBUS link on the Basic Operator Panel (BOP) frequently discover that well-known parameter numbers — most commonly P0700, P2040, and several fieldbus-monitor parameters — are not displayed at all. In some cases the drive also raises the PROFIBUS telegram-timeout fault F1910 repeatedly, or the PROFIBUS link locks itself at 187.5 kbit/s, which is far below the supported bus speed. The BOP is not broken, and the parameters have not been deleted; they are filtered out of the user-accessible parameter list by three internal parameters: p0003, p0010, and p0096.

This reference documents the exact cause of each filter, the firmware- and Control Unit-specific parameter restrictions that hide P0700 in particular, and the procedures that bring every expert parameter back into view. It also covers the recovery from F1910 and the underlying reasons a CU240 may stay at 187.5 kbit/s on PROFIBUS. Where the BOP is impractical, the article shows how to use STARTER, SINAMICS StartDrive, or the TIA Portal to confirm and override the same settings.

Why Parameters Disappear from the BOP

SINAMICS G120 uses a three-stage filter to decide which parameters are visible and writable from any operator panel. All three must permit access; if any one is restrictive, the parameter is removed from the BOP list even when it physically exists in the parameter set.

1. User Access Level — p0003

The default after factory reset is p0003 = 1 (Standard). If you do not raise this to 3, the BOP never displays PROFIBUS parameters P2020 and P2040 and most BICO parameters.

2. Commissioning Filter — p0010

If p0010 ≠ 0, most parameters — including P2040 and P0700 — are read-only or hidden. Many engineers are caught by the fact that p0010 stays at 1 (Quick commissioning) at the end of basic commissioning if a required entry was skipped. Returning to operation requires writing p0010 = 0 and confirming the drive state with p0003 = 3.

3. Application Class — p0096

The "Standard Drive" class (p0096 = 1) is the most common cause of "missing" parameters for users familiar with the full SINAMICS parameter set. Set p0096 = 0 to expose the expert view.

CU240B-2 / CU240E-2 Parameter Restrictions

Even with all three filters opened, certain parameters are physically absent on specific Control Unit variants. The CU240 family uses a streamlined parameter set to keep the firmware footprint manageable.

Restoring the Missing PROFIBUS Parameters on the BOP

Once the three filters are opened, the parameters expected by a PROFIBUS engineer are immediately reachable from the BOP. Sequence the writes carefully, because some writes are only accepted in a defined state.

Step 1 — Set expert access

On the BOP, navigate to p0003 and write 3:

Confirm with p0003 = 3 before continuing.

Step 2 — Exit commissioning filter

Read p0010. If it is not 0, write 0:

This returns the drive to the Run/Ready state and unlocks write access to P2040, P2020, and p0922.

Step 3 — Open application class

Read p0096. If 1 (Standard Drive), write 0:

Acknowledging the prompt (if any) and cycling 24 V control power are sometimes required for the parameter set to expand.

Step 4 — Verify PROFIBUS parameters are visible

Now navigate to:

• p0922 — PROFIBUS PZD telegram selection
• P2020 — PROFIBUS baud rate (DP units only)
• P2040 — Fieldbus monitoring time (ms)
• r2050, r2053 — PROFIBUS PZD receive / send words
• r0947 — Last fault code

If any parameter still does not appear, the BOP may be locked to a User-defined list — change p0003 = 0, accept the warning, then re-enter p0003 = 3. The BOP occasionally needs a power-cycle after a p0096 change to rebuild the parameter table.

P2040 — Fieldbus Monitoring Time

P2040 is the single most useful PROFIBUS timing parameter when F1910 is occurring. Increase P2040 to 100–200 ms while diagnosing the network, then tighten it once the PLC cycle, baud rate, and cable installation are validated. The Siemens PROFIBUS guideline recommends a value at least three times the PLC send cycle to absorb jitter.

F1910 — PROFIBUS Telegram Failure: Causes and Remedies

F1910 is raised when the Control Unit detects that no valid PROFIBUS PZD telegram has been received within P2040 ms. The most common root causes, in descending order of frequency, are:

1. PLC in STOP or the PROFIBUS master not sending cyclic data. Verify the PLC is in RUN and the PROFIBUS send clock is enabled (e.g. SFC14 / SFC15 with consistent slot configuration in STEP 7 / TIA Portal). Check r2050[0] — when telegrams arrive, the control word updates.
2. Baud-rate mismatch. A mismatch between master and slave locks the link at the lowest baud rate both ends support; verify P2020 against the PROFIBUS master project.
3. Cable / connector defects. Repeaters drawing too much current, missing termination, broken shield, or a segment longer than the maximum length for the configured baud rate. At 1.5 Mbit/s the maximum segment is 200 m; at 12 Mbit/s it is 100 m.
4. P2040 set too low for the PLC scan time. If the PLC OB1 cycle plus any watchdog is larger than P2040, F1910 will fire on every cycle. Use P2040 = 200 ms as a safe starting value, then reduce.
5. Slave address conflict. Two slaves with the same PROFIBUS address disrupt the token-passing protocol; check p0918.

PROFIBUS Baud Rate Stuck at 187.5 kbit/s

On SINAMICS G120 with CU240B-2 DP or CU240E-2 DP, the PROFIBUS baud rate is detected automatically from the master. If the drive stays at 187.5 kbit/s after the PLC goes RUN, two things should be checked:

• Read P2020. The default is P2020 = 0 (auto-detection). A locked value such as P2020 = 4 (which corresponds to 187.5 kbit/s in the SINAMICS baud-rate table) is a strong sign that someone has forced the slave to that speed.
• Check r2050[0] and the PROFIBUS diagnostics LED. If the cyclic I/O exchange is healthy, the drive negotiates up to the master's baud rate within a few seconds. If it stays at 187.5 kbit/s, the most likely cause is a weak signal — usually excessive stub length, missing termination, or a damaged connector. Inspect the 9-pin D-sub, verify the bus terminator is on at both ends only, and measure the A-B wire voltage (should be ≥ 1 V with a healthy differential).

On CU240E-2 DP, supported maximum is 12 Mbit/s. On CU240B-2 DP, the firmware typically supports up to 12 Mbit/s as well, but verify with the firmware version installed (r0018).

Alternative Commissioning Tools

If the BOP refuses to expose the parameters (for example, the BOP-2 is locked at a custom parameter list, or the drive is in a fault state that blocks parameter writes), use one of the following tools over USB, PROFIBUS, or PROFINET. Each can read p0003, p0010, and p0096 without going through the BOP.

Step-by-Step Recovery Procedure

1. Read the firmware version with r0018 and confirm the Control Unit model on the nameplate (e.g. 6SL3244-0BB12-1BA1 = CU240B-2 DP, FW 4.7).
2. On the BOP, navigate to p0003 and write 3.
3. Navigate to p0010 and write 0. If the drive rejects the write, clear any active fault with the FN key first.
4. Navigate to p0096 and write 0. If the BOP asks to confirm a change of parameter set, accept.
5. Cycle 24 V control power. The drive reboots and rebuilds the parameter table with the expert view.
6. Verify visibility of P2040, P2020, p0922, and p0015.
7. Set P2040 = 200 temporarily to absorb telegram jitter while commissioning the network.
8. Confirm the PROFIBUS master project telegram matches p0922 (e.g. 1 = Standard Telegram 1).
9. If P0700 is required by your documentation, replace it with the macro-based commissioning flow: select macro 7 (PROFIBUS control) or 15 (PROFIBUS with setpoint source) in p0015, then verify the BICO interconnections in p0840, p0852, p1035, p1036, p1070, and p1075.
10. Run the drive under PLC control. Reduce P2040 to a value ≈ 3× PLC send cycle once the network is healthy.
11. Save the parameter set to the drive non-volatile memory with p0977 = 1. A second save to an external MMC card with p0971 is recommended.

Verification Checklist

• p0003 = 3 after write — confirms expert access persisted.
• p0010 = 0 — drive is in Run/Ready.
• p0096 = 0 — application class is Expert.
• P2040 is visible and writable.
• p0922 matches the PROFIBUS telegram configured in the PLC project (1, 20, 352, or 999 for free BICO).
• r2050[0] reflects control word updates from the PLC.
• r0947 shows no active faults; if F1910 is the last fault, observe r0949[0] for the trigger cause.
• r0018 (Control Unit firmware) is recorded for the maintenance log.
• p0977 = 1 saves parameters; pull 24 V and confirm values persist after reboot.

Reference Parameter Table

Frequently Asked Questions