Resolving SIMOTION SCOUT D435 to D435-2 Message Frame Changes

When a SIMOTION D435 is swapped for a D435-2 inside a SIMOTION SCOUT 4.3 project, the message frame (telegram) configuration of the controller and the CX32-2 controller extension can be silently renumbered. The project still compiles, online connectivity is preserved, and there is no error or warning in the compile log, yet the drive and I/O slot mappings no longer match the source project. The root cause is the interaction between the symbolic I/O assignment setting, the Telegram mode (Manual versus Automatic) of the SIMOTION D, and the implicit remap that SCOUT performs when the controller type changes. This technical reference documents the root cause, the prerequisites, the step-by-step resolution, the verification procedure, and a troubleshooting matrix for engineers migrating SIMOTION D435 projects to D435-2.

Problem Description

Engineers who copy an existing SIMOTION SCOUT 4.3 project to migrate from a SIMOTION D435 to a D435-2 controller frequently report the following symptoms:

• Drive slot numbers in HW Config are renumbered after the controller swap.
• PROFIdrive telegrams (Standard Telegram 1, 2, 3, 4, 5, 6, 7, 9, Siemens Telegram 110, 111, and similar) are reassigned to different slots.
• The CX32-2 controller extension port assignments change in HW Config after the D435 to D435-2 swap.
• Symbolic I/O references in the SIMOTION program no longer resolve at runtime.
• Technology objects (TO) such as TO_Axis, TO_SynchronousAxis, TO_Encoder reference drive slots that no longer exist or that have moved.
• On commissioning, drives fault with PROFIdrive telegram mismatch (for example fault F08501 in the SINAMICS S120 drive).

The most dangerous aspect of this problem is that the SCOUT compile log shows zero errors and zero telegram-related warnings. The engineer only discovers the slot shift when a technology object fails to connect online, or when a drive refuses to come out of the start inhibit at runtime.

Root Cause Analysis

The message frame shift is driven by three independent SCOUT settings that interact when the controller type is changed:

1. Symbolic I/O assignment — decouples logical I/O names from physical slot positions.
2. Telegram mode — determines whether telegrams are pinned to specific slots (Manual) or freely reassigned (Automatic).
3. HW Config rebuild behavior — SCOUT regenerates the slot layout when the controller Order Number / Type changes.

SIMOTION SCOUT supports two I/O addressing modes for the SIMOTION D controller:

• Direct I/O addressing (slot-based): every I/O address is bound to a specific slot number in the rack.
• Symbolic I/O assignment (name-based): the program references logical names that are mapped to physical slots at compile time, independent of the slot position.

When symbolic I/O assignment is disabled, every I/O reference in the SIMOTION program is bound to a specific slot number. If the D435 and D435-2 have different internal slot layouts for the onboard PROFINET interface, for the drive interface, or for the CX32-2 controller extension connection, the message frame slots are renumbered when the controller is swapped.

New SIMOTION SCOUT 4.3 projects are created with symbolic I/O assignment enabled by default, but projects originally authored against an older SIMOTION D generation (D435, D445, D445-1) typically have symbolic I/O assignment disabled. When such a project is copied and the controller is swapped to D435-2, the direct addressing forces a slot renumber and the message frame configuration follows the slot renumbering.

In addition, the Telegram configuration property in HW Config can be set to either Manual or Automatic. In Automatic mode, SCOUT reassigns telegrams to the first free slot on the new controller. The recommended workflow during migration is to use the same Telegram mode (preferably Manual) in both the source and target projects so that message frames remain pinned to their original slots.

SIMOTION D435 vs D435-2 Architectural Differences

The D435-2 is the successor to the D435 in the SIMOTION D product line. The D435-2 is mechanically and electrically slot-compatible with the D435 inside a SINAMICS S120 line-up, but the internal PROFINET interface slot numbering, the default cyclic telegram assignments, and the way the controller extension ports are addressed differ from the D435. The CX32-2 controller extension replaces the older CX32 module, and like the D435-2, the CX32-2 has updated port assignments.

Because the slot and port numbering shift between D435 and D435-2, the controller extension upgrade (CX32 to CX32-2) and the SIMOTION D swap should be treated as a single coordinated change rather than two independent edits. Performing them in the wrong order forces SCOUT to remap the telegram slots manually, which is the most common cause of the silent message frame shift described in this article.

CX32 vs CX32-2 Controller Extension

The CX32 is a SIMOTION controller extension that adds distributed I/O and drive coupling to a SIMOTION D controller. The CX32-2 is the successor module that pairs with the SIMOTION D generation that includes the D435-2. The CX32-2 has the same mechanical form factor as the CX32, but the firmware version, port numbering, and default PROFIdrive telegram assignments differ. The migration sequence is:

1. Change the SIMOTION D type from D435 to D435-2 in HW Config.
2. Save and compile HW Config.
3. Close HW Config.
4. Let SCOUT update the project, including the automatic CX32 to CX32-2 conversion.

Do not delete the CX32 module and insert a CX32-2 module as an independent edit. The SCOUT automatic update path preserves the telegram slot assignments of the existing project; a manual delete-and-insert forces SCOUT to remap every drive telegram manually and is the most common cause of the message frame shift described in this article.

Symbolic I/O Assignment in Detail

Symbolic I/O assignment is the SCOUT project setting that decouples the I/O address seen by the SIMOTION program from the physical slot the module occupies. When enabled, the program references logical names such as driveAxis1.driveIf_STW1 or ioModule_slot3.inputWord0 rather than slot-pinned I/O addresses. The setting is stored in the SIMOTION project, not in the controller firmware, so it must be set on every engineering PC that opens the project.

To check the current setting, open SCOUT and click the project root in the project navigator. Open the project menu. The Use symbolic assignment option should be ticked. If the option is greyed out, close all open editors, click on the project root, and re-open the project menu.

Telegram Configuration Modes

The Telegram mode setting in HW Config controls how SCOUT places PROFIdrive telegrams on the slots of the SIMOTION D and the CX32-2 controller extension. There are two modes:

• Manual — telegrams are pinned to the slot positions defined in HW Config. Manual mode is the only mode that guarantees identical telegram slot layout before and after a D435 to D435-2 swap.
• Automatic — SCOUT places telegrams on the first free slot that fits the telegram type. After a controller swap, SCOUT may re-place telegrams to fit the new slot layout. The compile log will not show a warning.

The PROFIdrive telegrams used by SIMOTION drives in this class of application are typically:

After the D435 to D435-2 swap, verify that every drive is still on the same telegram as in the source project. If the Telegram mode was set to Automatic, SCOUT may have moved telegrams around to fit the new slot layout.

Prerequisites

Before applying the resolution procedure, confirm the following:

• SCOUT 4.3 (or a compatible 4.x version) is installed with the latest hotfix.
• The D435-2 firmware is compatible with the installed SCOUT version. Verify the compatibility matrix in the Siemens Industry Online Support portal.
• The CX32-2 firmware is compatible with the D435-2 firmware and with SCOUT 4.3.
• STEP 7 / SIMATIC Manager is available because the HW Config edit is performed in SIMATIC Manager, not in SCOUT itself.
• A complete project backup (ZIP archive) exists for rollback.
• The user has the project rights to change HW Config and to recompile the SIMOTION project.
• The PROFINET device name and IP address of the D435-2 are known and available for assignment after the swap.

Step-by-Step Resolution Procedure

The procedure below restores the original message frame layout and prevents the silent telegram shift when migrating a SCOUT 4.3 project from D435 to D435-2.

Step 1 — Save the Source Project Under a New Name

Open the original SCOUT 4.3 project. Use Project > Save As to save a copy of the project under a new name. Never perform the hardware swap on the only copy of the project. The original ZIP archive serves as the rollback baseline.

Step 2 — Enable Symbolic I/O Assignment

Open SCOUT and click the project root in the project navigator. Open the project menu and tick Use symbolic assignment. Confirm any dialog that SCOUT displays. This setting decouples logical I/O names from physical slot positions and is the single most important setting for preventing silent telegram shifts during a controller swap.

Step 3 — Save and Recompile the Project

Save the SCOUT project and trigger a full recompile of the SIMOTION program. The recompile forces the I/O references in the source to be remapped to symbolic names. Resolve any compile errors before proceeding to the hardware swap.

Step 4 — Open HW Config and Replace D435 with D435-2

Open SIMATIC Manager and open the HW Config of the SIMOTION PLC. Right-click the D435 module and change the Order Number / Type to the D435-2. Save and compile the HW Config, then close HW Config.

Do not touch the CX32 module at this point. SCOUT will update the CX32 module to CX32-2 automatically once it detects the D435-2 in the configuration.

Step 5 — Allow SCOUT to Update the Project

Switch back to SCOUT. SCOUT will prompt to update the project to the new controller type. Click Yes. When SCOUT asks to switch to symbolic I/O assignment, click Yes again to confirm. The automatic update path converts the CX32 module to CX32-2 and preserves the original telegram slot assignments of the project.

Step 6 — Verify the Telegram Configuration

Open HW Config again and inspect the Telegram settings on every drive and on the CX32-2 port. Confirm that the telegrams are still the same PROFIdrive telegrams (Standard Telegram 1/2/3/4/5/6/7/9 or Siemens Telegram 110/111) that were used in the source project. If SCOUT has flipped the Telegram mode from Manual to Automatic, set it back to Manual so the slots stay pinned.

Step 7 — Recompile and Download

Recompile the SIMOTION project in SCOUT and download the project to the D435-2. Perform a CPU restart and a non-volatile card check. Verify that the D435-2 retains the project across a power cycle.

Working Code — Symbolic I/O References in Structured Text

When symbolic I/O assignment is enabled, the SIMOTION program can reference drive I/O symbolically. The code fragment below shows the ST pattern for reading a drive status word and writing a control word using the symbolic I/O name assigned in HW Config.

// SIMOTION ST example: symbolic drive I/O access (SCOUT 4.3)
// I/O names assigned in HW Config under symbolic I/O assignment

IF driveAxis1.driveIf_STW1.servoReady = TRUE THEN
    // drive is ready, request ramp-up
    driveAxis1.driveIf_STW1.on         := TRUE;
    driveAxis1.driveIf_STW1.ackFault   := FALSE;
    driveAxis1.driveIf_STW1.off1       := FALSE;
END_IF;

IF driveAxis1.driveIf_ZSW1.ackFaultPending = TRUE THEN
    // drive reported a fault, send acknowledgement
    driveAxis1.driveIf_STW1.ackFault   := TRUE;
END_IF;

// Read telegram diagnostics
myTelegramDiag.stw1 := driveAxis1.driveIf_STW1;
myTelegramDiag.zsw1 := driveAxis1.driveIf_ZSW1;
myTelegramDiag.nset := driveAxis1.driveIf_NSET;
myTelegramDiag.nact := driveAxis1.driveIf_NACT;

Verification Procedure

After applying the resolution, perform the following checks to confirm that the message frame configuration survived the swap without silent shifts:

1. Open HW Config and confirm the D435-2 is in slot 0 of the rack and the CX32-2 is in the correct slot.
2. For each drive, confirm the telegram number matches the source project (e.g. Standard Telegram 5 on drive 1, Standard Telegram 6 on drive 2).
3. In SCOUT, compile the project and check the compile log for warnings.
4. Go online with the D435-2 and verify that every technology object (TO) resolves to the expected drive slot.
5. Trigger a CPU restart and confirm the drives come up in the correct order.
6. Run a single-axis jog to confirm cyclic PROFIdrive communication is healthy.
7. Use PRONETA to validate the PROFINET topology and the device name assignment of the D435-2.

Troubleshooting Matrix

Best Practices for SIMOTION D Hardware Migrations

• Always use Project > Save As to create a copy of the project before any hardware swap. The original ZIP archive is the rollback baseline.
• Enable Use symbolic assignment before changing the SIMOTION D controller type. This is the single most important preventive step.
• Change the SIMOTION D type first and let SCOUT update the CX32 to CX32-2 automatically. Do not delete and re-insert the controller extension manually.
• Avoid the Telegram mode = Automatic setting during a hardware migration. Switch to Manual for the migration, then re-evaluate after the controller is in production.
• Document the telegram layout (telegram number, slot number, I/O address range) of every drive in the project before the swap. The post-swap verification step has to be compared against this baseline.
• Use PRONETA to validate the PROFINET topology, device names, and IP addresses after the swap.
• Re-flash the CF card with a known-good image if the project is moved between controllers of different firmware versions.
• Cross-reference the Siemens Industry Online Support compatibility matrix for SCOUT version, D435-2 firmware, and CX32-2 firmware before performing the migration.

Field-Commissioning Notes

When the migration is performed in the field rather than in the office, the verification step is even more important because the engineer cannot always compare the HW Config against the source project offline. The following field checklist has been proven on production D435-2 migrations:

1. Save the project backup on a USB stick or a network share before any edit.
2. Go online with the D435-2 and dump the actual telegram configuration with the Accessible Nodes view in SIMATIC Manager.
3. Compare the dumped telegram configuration against the HW Config slot list. Any discrepancy is a silent slot shift.
4. If a discrepancy is found, abort the migration and re-do the seven-step procedure above.
5. After the migration, perform a controlled stop and start of every drive and confirm that no drive reports F08501 (telegram failure) on the SINAMICS S120 drive.

FAQ