Resolving SIMOTION D445 Alarm 1902 TMAPC Cycle Time Configuration

Alarm 1902 on SIMOTION D445: System Overview

Alarm 1902 is a configuration-class fault reported by the SIMOTION D445 motion controller when one or more technology objects (TOs) cannot be brought into a consistent, runnable state. The alarm typically appears in the SIMOTION SCOUT diagnostic buffer shortly after project download, restart, or warm reset, and frequently points to a mismatch between the master application cycle time (TMAPC), the configured technology objects, and the available CPU bandwidth of the D445 module. When the alarm is cleared by editing the TMAPC value in the SIMATIC hardware configuration (HW Config) and re-downloading the station, the underlying cause is almost always an over-aggressive cycle-time configuration that the D445 cannot honor on its current technology object load.

The D445 is part of the SIMOTION D drive-based controller family and combines a SIMOTION runtime with the backplane of a SINAMICS S120 line module. It runs the SIMOTION kernel on top of a SINAMICS CU320-2 control unit, with technology objects bound to the drives on the same DRIVE-CLiQ network. Because the SIMOTION task system, the SINAMICS Servo/Vector control, and the technology objects all share the same processor resources, cycle-time relationships inside the project must be dimensioned in accordance with the SIMOTION D4x5 Commissioning and Hardware Installation Manual.

SIMOTION D445 Cycle Architecture and the TMAPC Parameter

The SIMOTION D445 task system is a four-level time hierarchy. Every level has a defined role, and integer ratios between the levels are mandatory. The hierarchy is:

1. Servo cycle (TServo) – the fastest deterministic level, drives the SINAMICS setpoint interface (typically 250 μs, 500 μs, or 1 ms on D445).
2. IPO cycle (TIPO) – runs the interpolator for axes, cams, paths, and synchronous operations (typically 1, 2, or 4 ms).
3. IPO2 cycle (TIPO2) – a coarser interpolation level for technology objects that do not require servo-rate updates (typically 4, 8, or 16 ms).
4. TMAPC – Master application cycle time – the slowest deterministic level, runs the user MCC/LAD/FBD/ST program and non-time-critical I/O. The user program scheduling clock is based on TMAPC.

TMAPC is the cycle time of the highest-level BackgroundTask or the user-program task system root. It is configured in the SIMOTION SCOUT project tree under Execution system > Tasks, or equivalently, in HW Config of the SIMATIC manager / TIA Portal on the D445 properties dialog. On the D445, valid TMAPC values are restricted to the supported task grid:

Two integer-ratio conditions must always hold:

• TIPO / TServo = n (integer)
• TIPO2 / TIPO = m (integer)
• TMAPC / TIPO2 = k (integer, recommended; not strictly enforced but mandatory for BackgroundTask alignment)

The D445-2 supports minimum servo cycles down to 250 μs when fewer than four axes are configured, and 500 μs for full axis loading. The selection of TMAPC is independent of the servo rate but it influences the user program budget. A TMAPC of 1 ms is supported on D445-2 hardware, but only if the technology object load, IPO and servo configuration, and the configured SINAMICS objects fit within the deterministic execution window. When these conditions are not met, the system rejects the configuration with Alarm 1902.

Root Cause: Why 1 ms TMAPC Triggers Alarm 1902

Alarm 1902 is reported by the SIMOTION runtime when a configuration download, restart, or reinitialization of a technology object cannot be completed because the cycle-time grid is not feasible for the current project. Three underlying causes are most frequent:

1. Undersized TMAPC relative to TO load – A 1 ms TMAPC gives the D445 a 1 ms user program budget. If the project includes several axes, cams, paths, and measurement inputs, the BackgroundTask cannot complete, and the system refuses to enter RUN with Alarm 1902.
2. Invalid integer ratios – A TMAPC change in SCOUT can leave a non-integer ratio between TMAPC and TIPO2/TIPO, which the kernel refuses. Alarm 1902 then appears with additional detail indicating a “cycle grid violation”.
3. Drive or topology mismatch – When a SINAMICS S120 drive on DRIVE-CLiQ has its own servo cycle offset that does not match the SIMOTION task grid, the technology object configuration cannot be activated. The alarm is reported against the offending TO.

In the field case described here, the operator reduced TMAPC to 8 ms. This is a typical value for D445 systems with moderate TO loading and is fully compatible with the standard 1 ms Servo / 2 ms IPO / 4 ms IPO2 / 8 ms TMAPC grid (ratios 1:2:2:1). The alarm cleared because the configuration was finally within the valid grid and within the D445 execution budget.

TMAPC, TServo, TIPO, and TIPO2: Parameter Relationships

The four cycle-time parameters live in two locations in the engineering toolset:

• SIMATIC HW Config / TIA Portal device configuration – D445 properties dialog, “Cycle times” tab. The values entered here become the configured values that the SIMOTION kernel reads at boot.
• SIMOTION SCOUT – Execution system > Tasks. The values shown here are synchronized from the HW Config but can be viewed and used for task assignment of MCC/LAD/FBD programs.

It is critical to understand that TMAPC set in HW Config is the authoritative value. Changes made in SCOUT (for example, when assigning a program to a task) do not change TMAPC; they only bind a program to the existing cycle. To change TMAPC itself, the edit must be performed in HW Config and downloaded to the target station.

A safe starting grid for a D445 with SINAMICS S120 and 4–8 servo axes is:

TServo = 1.0 ms
TIPO   = 2.0 ms
TIPO2  = 4.0 ms
TMAPC  = 8.0 ms

Heavier axis counts or kinematics (cam, path, gearing objects) typically require TMAPC of 4 ms or 8 ms. Going below 4 ms TMAPC on a fully loaded D445 is rarely possible and should be avoided unless runtime measurements prove the budget is satisfied.

SINAMICS S120 Drive Integration and Alarm Propagation

The D445 is not a standalone controller; it is a SIMOTION runtime that runs on the same hardware as a SINAMICS CU320-2 control unit. This means that the SIMOTION task system and the SINAMICS drive firmware share the same processor and memory. The relevant integration points are:

• DRIVE-CLiQ topology – The D445 is on the same DRIVE-CLiQ ring as the SINAMICS Line Module, Motor Modules, and any SMC/SME sensors. The drive objects (DOs) are visible to the SIMOTION technology objects as axes.
• Setpoint interface – The SIMOTION Servo task issues setpoints to the SINAMICS Servo at the configured TServo. Mismatches between TServo and the SINAMICS sampling time (p0115) lead to alarm propagation back to SIMOTION, sometimes surfacing as Alarm 1902 on the axis TO.
• Topology configuration – The SIMOTION project references the SINAMICS DO by topology. When DRIVE-CLiQ wiring changes, the topology must be reloaded to both the D445 and the SINAMICS, in the same sequence: SINAMICS first, then SIMOTION.

For the SINAMICS S120 Drive Functions Manual integration, ensure that:

1. p0115[0] (current controller cycle) matches the SINAMICS firmware capability of the Motor Module.
2. p0115[1] (speed controller cycle) is consistent with the SIMOTION TServo.
3. p0099 (sampling time synchronization) is correctly aligned between the D445 and SINAMICS.

Resolution: Correct TMAPC Configuration Procedure

The correct sequence to change TMAPC and clear Alarm 1902 is the following. The operator who changed TMAPC in HW Config and downloaded performed the first half of the procedure correctly; the second half (persistence) is where the issue remained.

1. Open the SIMOTION project in SIMOTION SCOUT.
2. Open the SIMATIC station in HW Config (right-click D445 > Open HW Config, or use TIA Portal device configuration for the D445).
3. Open the D445 properties > Cycle times tab.
4. Set TMAPC = 8.0 ms (or another supported value that satisfies integer ratios).
5. Verify the integer ratios: TIPO/TServo, TIPO2/TIPO, TMAPC/TIPO2 must all be integers.
6. Click OK and recompile the station.
7. In HW Config, select the SIMATIC station and execute Target system > Load to target station (or Download to device in TIA Portal).
8. Wait for HW Config download to complete. The D445 performs a restart.
9. Return to SIMOTION SCOUT. Execute Target system > Download > Download to target for the SIMOTION project.
10. When the SCOUT download dialog appears, ensure the Copy RAM to ROM option is checked. This writes the new configuration to the non-volatile memory (CompactFlash card) of the D445.
11. Confirm download and wait for the D445 to enter RUN.
12. Verify the alarm is no longer present in the SCOUT alarm buffer.
13. Perform a power-cycle test: turn the D445 off, wait for the CF card LED to extinguish, power on, and confirm Alarm 1902 does not reappear.

Step 10 is the persistence step. If you skip it, the change lives in volatile memory only, and the next restart reverts to the configuration stored on the CF card, which still contains the old 1 ms TMAPC value. This is the exact failure mode that the operator experienced: each power-cycle reloaded the original 1 ms TMAPC from the CF card and re-raised Alarm 1902.

Persistence: CompactFlash Card, RAM, and ROM Strategy

The SIMOTION D445 boots from a CompactFlash (CF) card. The card is the non-volatile image of the runtime and the project. Three storage areas are in play:

• CF card (non-volatile) – The persistent project image. Loaded on every power-on. This is what survives the blackout.
• RAM (volatile) – The runtime working memory. Downloads to the target station write to RAM only.
• ROM (non-volatile, write-once-style) – The destination of “Copy RAM to ROM”. Operationally identical to writing to the CF card.

The flow is:

The diagram illustrates why the operator’s initial fix worked once but failed after a power-cycle. The HW Config change was downloaded to RAM, the alarm cleared, but Copy RAM to ROM was either not performed or not persisted, so the CF card still held the old 1 ms TMAPC image. After a blackout, the D445 reloaded from the CF card and the alarm reappeared.

To make TMAPC changes durable:

1. Use Target system > Copy RAM to ROM in SCOUT after the HW Config download and the SCOUT project download.
2. Alternatively, use the SCOUT menu Target system > Load > Download to target and tick Copy RAM to ROM in the dialog. This single operation downloads and persists in one step.
3. For sites with frequent power loss, consider a UPS on the D445’s 24 V supply to give the controller time to complete internal flush operations during shutdown.

A second persistence mechanism exists for the SIMOTION project itself: the Project comparison function in SCOUT can be used to verify that the project on the engineering PC matches the project image stored on the CF card. If the comparison reports a difference after a power-cycle, the CF card image has not been updated and a fresh Copy RAM to ROM is required.

Step-by-Step Commissioning and Download Procedure

For engineers encountering Alarm 1902 for the first time on a SIMOTION D445 + SINAMICS S120 system, the following commissioning sequence avoids the persistence pitfall.

Prerequisites

• SIMOTION SCOUT (version matched to D445 firmware; e.g. SCOUT V4.5 for D445 firmware V4.5, or SCOUT V5.x for D445-2 firmware V5.x). Check compatibility in the SIMOTION SCOUT / D4x5 compatibility matrix.
• STEP 7 V5.5+ or TIA Portal V14+ with the SIMOTION option package.
• Access to the D445 via PROFIBUS or PROFINET with the correct IP address. Default PROFINET device name is empty; configure before download.
• A confirmed working backup of the original project on a network share.

Procedure

1. Open the SIMOTION project in SCOUT and Save As a working copy.
2. Open HW Config from the SIMATIC station.
3. Double-click the D445 module and open the Cycle times tab.
4. Set TMAPC to 8.0 ms (or 4.0 ms if your project and load profile allow). Confirm the integer ratios are satisfied.
5. Close the dialog with OK, save, and recompile the station (Station > Save and Compile).
6. Select the SIMATIC station and choose Target system > Load to target station. Confirm the prompt. The D445 performs a restart.
7. After the restart, return to SCOUT. Select the SIMOTION device and choose Target system > Download > Download to target.
8. In the download dialog, tick Copy RAM to ROM. Click OK.
9. Wait for the download to complete. SCOUT will report the new state of the device (RUN/STOP).
10. Open the Alarm buffer in SCOUT (Project navigator > SIMOTION device > Diagnostics > Alarm buffer). Verify Alarm 1902 is not present.
11. Issue a restart to the D445 (Target system > Restart (warm reset)). Re-verify the alarm buffer.
12. Issue a power-cycle: turn the D445 off at the 24 V supply, wait at least 30 seconds, then power it on. Re-verify the alarm buffer after boot.

Verification Checklist

Verification Checks and Diagnostic Buffer Analysis

If Alarm 1902 persists after the procedure, collect the following data from the SCOUT diagnostic buffer and the SINAMICS diagnostic buffer before re-attempting the download:

1. Alarm buffer in SCOUT > SIMOTION device > Diagnostics. Record the full text, the affected technology object, the timestamp, and any associated clear information.
2. Diagnostic buffer of the D445 (CPU > Module Information > Diagnostic Buffer in STEP 7 or TIA Portal). This contains kernel events that precede the user-visible alarm.
3. Diagnostic buffer of the SINAMICS CU320-2 (online via SCOUT > Drive > Diagnostics > Buffer). The drive-side events can confirm whether a Servo or IPO mismatch is the root cause.
4. Task runtime measurement in SCOUT > Execution system > Task runtimes. If any task reports >80% utilization, the cycle is undersized and TMAPC must increase further.

The diagnostic buffer entry for Alarm 1902 typically reads:

1902 <TO_name> Configuration error:
Cycle time grid invalid or insufficient CPU resources
for the configured technology object set.

If the diagnostic buffer references a specific technology object (e.g. Axis1, Path1, Cam1), the configuration of that TO is the primary suspect. Open the TO in SCOUT and check its expert list for the ipoCycleTime, servoCycleTime, and ipo2CycleTime values. All three must align with the TMAPC/IPO/IPO2 grid set in HW Config.

Related Technology Object Configuration

Beyond TMAPC, several other SIMOTION technology-object parameters interact with the cycle grid and can surface as Alarm 1902 if misconfigured. The most common are:

For a more comprehensive list of D445 technology-object limits, refer to the SIMOTION D4x5 Function Manual, which enumerates the maximum number of axes, cams, paths, and TO instances for each D445 variant (D445-1, D445-2 DP, D445-2 PN/PN).

Compatibility and Firmware Notes

The D445 firmware version must be compatible with the SIMOTION SCOUT version used. Mismatched versions are a common source of configuration errors that look like Alarm 1902 but are actually download-time version mismatches. The relevant compatibility points are:

• SCOUT V4.4 supports D445-1 with firmware V4.4.
• SCOUT V4.5 supports D445-1 and D445-2 with firmware V4.5.
• SCOUT V5.1/V5.2/V5.3/V5.4 support D445-2 only (D445-1 reaches end of support).
• Always check the SIMOTION SCOUT readme for the supported firmware list before upgrading either SCOUT or D445 firmware.

When changing the TMAPC of a running production system, plan a maintenance window. The HW Config change forces a full restart of the D445 and an interruption of the SINAMICS S120 drive control. Field devices and connected drives must be in a safe state before download.

Common Pitfalls and Field Notes

• Editing only in SCOUT – SCOUT cannot change TMAPC. The TMAPC value is read-only inside the SCOUT project view; it is set in HW Config. Engineers who try to change TMAPC inside SCOUT will see the value “reset” on the next HW Config read, often mistaking the behavior for a download issue.
• Skipping Copy RAM to ROM – The most frequent cause of a TMAPC change that does not survive a power-cycle. The fix is mechanical: tick the box in the SCOUT download dialog.
• Forgetting the SINAMICS download – If the SINAMICS topology or sampling time was changed, the SINAMICS download must precede the SIMOTION download. Reversing the order can leave the D445 with a referenced DO that does not exist, surfacing as Alarm 1902 on the affected axis TO.
• Lowering TMAPC below the default to chase throughput – Unless runtime measurements show headroom, lowering TMAPC is a common anti-pattern. The D445 is designed for moderate-to-heavy motion load at the standard 8 ms TMAPC grid; faster cycles are useful only for very light axis counts.
• Compiling only the SIMOTION side – A TMAPC change in HW Config must trigger a SIMATIC station recompile. If only the SIMOTION side is compiled, the HW Config change is not propagated and the runtime will load the old value.

Summary of the Recommended Configuration

For a SIMOTION D445 controlling SINAMICS S120 drives with 4–8 axes and standard technology objects, the recommended starting grid is:

This grid clears Alarm 1902 in the typical case, survives power-cycles once persisted with Copy RAM to ROM, and provides sufficient CPU budget for the standard technology object load of a D445-2 system. Heavier systems may require TMAPC of 16 ms and IPO2 of 8 ms; lighter systems can use TMAPC of 4 ms. Profile the runtime after any change using the SCOUT task runtime measurement tool before declaring the configuration stable.