Resolving SINAMICS S120 F1420 with Heidenhain EQN 1336S Encoder

Problem Description: F1420 on SINAMICS S120 with Heidenhain EQN 1336S

During commissioning of a SINAMICS S120 drive line-up based on a CU320-2 control unit running firmware V5.1.1.12, configuring a Heidenhain EQN 1336S absolute rotary encoder triggers fault F1420 "Component Difference" (or "Component difference in the encoder interface") every time the drive is switched on. The fault is generated regardless of which of the standard p0400 encoder codes is loaded into the drive object:

• p0400 = 204 (EnDat 2.1 sin/cos 1 Vpp, no commutation)
• p0400 = 214 (EnDat 2.2 sin/cos 1 Vpp, no commutation)
• p0400 = 224 (EnDat 2.1 sin/cos with commutation track)
• p0400 = 244 (EnDat 2.2 sin/cos with commutation track)
• p0400 = 10058 (third-party / non-listed code)

The drive remains uncommissionable; the encoder is shown in the STARTER / Startdrive topology view with a yellow question mark, indicating that the control unit cannot identify the encoder interface module. The associated fault buffer value read from r2124 is 17040409 (decimal), and the message identifier is 1420. F1420 keeps the drive in "commissioning required" state and blocks pulse enable until the discrepancy between the configured component and the physically detected component is resolved.

System Architecture: SINAMICS S120, CU320-2, and the EQN 1336S

The Heidenhain EQN 1336S is a multiturn absolute rotary encoder with the following relevant characteristics for a SINAMICS S120 integration:

The CU320-2 is the central control unit for the S120. It is connected to a Line Module (infeed), one or more Motor Modules, and any associated Sensor Modules (SMC) via DRIVE-CLiQ. The EQN 1336S does not have a native DRIVE-CLiQ interface, so the encoder must be wired to a Sensor Module Cabinet (SMC) that translates EnDat to DRIVE-CLiQ. For an EnDat 2.1 sin/cos encoder, the correct SMC is the SMC20 (Sensor Module Cabinet 20).

F1420 "Component Difference" – Definition and Sub-Codes

F1420 is raised by the SINAMICS firmware when the component type, article number, or vendor identifier that the drive object has in its offline configuration does not match the component that is electrically present and responding on the relevant DRIVE-CLiQ node. The full message is typically:

F1420 (N, A) Component difference: Component number %1, component type %2, connection number %3, reference %4

On SINAMICS S120, the fault can originate from:

Decoding r2124 = 17040409

The fault value stored in r2124 (or r0949 for the same fault) is a 32-bit integer that Siemens encodes with the cause, the affected drive object, and the connection number. The value 17040409 decimal equals 0x0104_0409 in hexadecimal. Decoding in the way Siemens publishes in the S120 List Manual:

The most actionable read of the value is "the drive object expected an SMC20 or another encoder interface at the encoder connection, but what is sitting at that DRIVE-CLiQ port either is not the right type or does not respond correctly as an encoder." This is why changing p0400 alone does not clear the fault – the issue is at the component / topology level, not the encoder-code level.

p0400 Reference: Encoder Selection Codes for EnDat on SINAMICS S120

p0400[0..n] (Encoder type selection) is an indexed parameter that maps a numeric code to a specific encoder vendor / protocol / resolution. The List Manual lists the values supported by the firmware version in use. For EnDat 2.1/2.2 sin/cos encoders on firmware V5.1, the typical codes are:

The codes 204 / 214 assume a sin/cos encoder without a separate commutation track. The codes 224 / 244 are for sin/cos encoders with a commutation track. The EQN 1336S has integrated commutation (commutation is derived from the absolute position), so either no-commutation or with-commutation codes may be valid depending on how the drive uses the C/D signals on the SMC20. If the Heidenhain datasheet for the specific EQN 1336S variant states "EnDat 2.1 with incremental signals 1 Vpp", 224 is the correct choice on firmware V5.1. If the datasheet states "EnDat 2.2", 244 applies. The List Manual for firmware V5.1 lists the exact resolution associated with each code; the encoder's singleturn / multiturn resolution in p0421 / p0422 must match the EQN 1336S nameplate (29 / 12 bits).

DRIVE-CLiQ Topology Rules and the "Yellow Question Mark"

When STARTER / Startdrive displays the encoder with a yellow question mark under the Topology tab, it means the offline configuration does not have a component object at that DRIVE-CLiQ port, or the component object that is there does not match what the firmware has discovered online. The most common reasons for this on a Heidenhain EQN 1336S configuration are:

1. The SMC20 is missing from the offline project. STARTER only knows about the components that were added to the project. If no SMC20 was inserted into the topology tree (right-click → "Insert new component → Sensor Module Cabinet 20"), the firmware finds the device at the DRIVE-CLiQ port but cannot bind it to a drive object.
2. The SMC20 is on the wrong port. SMC20s are typically connected to the encoder port of the Motor Module (X22 on most MM types), not the DRIVE-CLiQ port of the CU.
3. The Motor Module itself is not commissioned. If the Motor Module's drive object has not been auto-configured, every component downstream of it appears as unknown.
4. The Drive Object is mis-numbered. When using a CU320-2 with no Line Module, the first Motor Module must be assigned to DO 2 (Servo) or DO 11/12 (Vector), depending on the commissioning wizard. A wrong number causes the encoder to be looked up under a non-existent DO.

Worked procedure to clear a yellow question mark:

1. Right-click the Control Unit and choose Automatic configuration → Activate (or Automatic device configuration in Startdrive).
2. Let STARTER detect the actual DRIVE-CLiQ topology, then compare it to the offline project.
3. Manually correct any missing or wrong components so the offline topology matches the online detection 1:1.
4. Save the project to the PG/PC and download it to the CF card of the CU320-2.
5. Power-cycle the drive line-up.

SMC20: The Required Interface for EnDat 2.1/2.2 sin/cos Encoders

The SMC20 (Sensor Module Cabinet) is the only cabinet-mounted Sensor Module that supports EnDat 2.1/2.2 combined with 1 Vpp sin/cos incremental signals. Key characteristics:

The SMC20 must be physically present at the encoder port of the Motor Module, and the offline project must have an SMC20 object inserted at the same DRIVE-CLiQ node. If the project has the wrong SMC type (e.g., an SMC30, which is for TTL/HTL/SSI), the firmware will raise F1420 because the component article number does not match.

Commissioning Procedure: EQN 1336S on CU320-2 V5.1.1.12

Use the following procedure in STARTER V5.4 (or Startdrive in TIA Portal, but the project used in the original case was STARTER V5.4):

1. Open the project and go online. Connect STARTER to the CU320-2 over PROFIBUS, PROFINET, or Ethernet, then right-click the CU and choose Connect to target system → Online.
2. Upload the actual topology. Right-click the CU, Target device → Upload from device (RAM to ROM). This pulls the real DRIVE-CLiQ topology from the CU.
3. Insert missing components. If the SMC20 does not appear in the offline topology, right-click the Motor Module → Insert new component → Sensor Module Cabinet 20. Set the port number to the physical DRIVE-CLiQ port on the Motor Module (typically X22 for the encoder interface).
4. Set p0400 on the affected drive object. Open the drive object that owns the encoder, navigate to Configuration → Encoder, and set p0400 to the correct EnDat code:
   • p0400[0] = 244 if the EQN 1336S is EnDat 2.2 with commutation.
   • p0400[0] = 224 if the EQN 1336S is EnDat 2.1 with commutation.
5. Set p0400 = 9999 first as a diagnostic baseline. If F1420 still appears with p0400 = 9999, the problem is not the encoder code; the problem is the topology. Do not waste time cycling p0400 values if p0400 = 9999 already triggers F1420.
6. Verify the encoder nameplate parameters. After selecting the encoder code, STARTER writes the default singleturn / multiturn resolution and inversion to the drive. Compare:
   • p0421[0] (singleturn resolution) should equal 29 bits for the EQN 1336S.
   • p0422[0] (multiturn resolution) should equal 12 bits.
   • p0423[0] (fine resolution for position) is typically 20 bits for the SMC20 with 1 Vpp sin/cos.
7. Save and download. Right-click the drive object → Copy RAM to ROM, then Load to target device. Confirm the download completes without further F1420 / A1420 messages.
8. Power-cycle. Switch the line supply OFF, wait at least 30 seconds for the DC bus to discharge, then switch ON. The control unit boots with the new project and performs a fresh encoder initialization.
9. Check the fault buffer. After power-up, open Diagnostics → Fault buffer and confirm that F1420 no longer appears. The drive should go to "Commissioned" state.

Verification and Acceptance Test

Once F1420 is cleared, perform a structured acceptance test to confirm the encoder is working at the SINAMICS level:

1. Encoder status word: Read r0480 (encoder status word Gx_ZSW). Bit 0 (encoder ready) must be set, and bit 1 (parking not active) must be set. Bits 12/13 (function safety status) are not relevant for an SMx without PROFIsafe.
2. Position actual value: Read r0482[0] (encoder position actual Gx_XIST1). The value must track physical shaft rotation, in fine-resolution units (24 bits = 16,777,216 per revolution at the default fine resolution).
3. Velocity actual: Read r0061 (speed actual). At standstill, the value must be near 0 rpm, with jitter below the configured p4649 threshold.
4. Commutation accuracy: With the motor de-energized and the holding brake open, manually rotate the shaft one full revolution. The commutation offset p0431 (or p1011 for induction motors) must remain stable. If commutation shifts, the absolute encoder may be losing a count; check the EnDat cable shielding.
5. Endat init status: Read r0403[0] (encoder type of operating mode). The display should read "EnDat 2.1 sin/cos" or "EnDat 2.2 sin/cos" depending on the connected EQN 1336S variant.
6. Topology online vs. offline match: Right-click the CU → Topology. The SMC20 and the EQN 1336S (displayed as the encoder type) must show no yellow question mark. The order numbers and firmware versions should match the components in the cabinet.

Common Pitfalls and Field Notes

The original case report contains several patterns that are easy to repeat in the field. The most common are listed here so that subsequent engineers do not re-introduce the same issues:

• Setting p0400 without checking the topology. All five of the values 204 / 214 / 224 / 244 / 10058 raised F1420 in the original report. The reason is not that the codes are wrong – it is that the topology was not corrected first. If the offline project has no SMC20, the drive will raise F1420 no matter which EnDat code is selected. Always start with p0400 = 9999 and confirm the fault is reproducible.
• Using a non-standard p0400 like 10058. Codes above 10000 on the S120 are typically reserved for user-defined third-party encoders with a manufacturer-specific electronic nameplate (via p0440 / p0447). Without that nameplate properly loaded, the firmware cannot decode the encoder and raises F1420. Do not guess a code outside the standard List Manual list.
• Confusing the SMC and the Sensor Module Integrated (SMI). Some motors come with an SMI mounted directly on the motor, which is a DRIVE-CLiQ device. The EQN 1336S is a cabinet-mounting encoder without DRIVE-CLiQ, so it must go through a separate SMC20. Inserting an "SMI 20" or "SMI 30" into the offline project instead of an SMC20 will raise F1420.
• Misreading r2124 as a single number. The fault value is a packed field. Engineers sometimes look at "17040409" and think it is a single large identifier, then chase non-existent error codes. The correct read is the byte-wise split shown in the decoding table above.
• Skipping the power-cycle. After changing p0400, some firmware versions cache the encoder identification for the duration of the active session. A "warm restart" (p0970 = 1 alone) is not always sufficient. Power-cycle the line supply to force a cold re-init of the encoder interface.
• Mixing up C/D and A/B wiring. The EQN 1336S has both EnDat data lines and sin/cos 1 Vpp lines. If the cable is wired correctly for a Heidenhain pure-digital cable, the SMC20 will see both tracks. If the cable is wired as SSI-only (no A/B), the drive may show "SSI" instead of "EnDat sin/cos" in r0403.

Standard Document References (Verification)

Before accepting the fix, always verify the configuration against the current Siemens documentation. The two key documents are:

• SINAMICS S120/S150 List Manual – parameter descriptions, fault / alarm list with the exact r2124 layout for F1420. Available on Siemens Industry Online Support – SINAMICS S120/S150 Manuals.
• SINAMICS S120 Commissioning Manual – topology configuration, DRIVE-CLiQ wiring rules, Sensor Module selection, p0400 code tables. Available on the same SINAMICS S120/S150 product page.
• Heidenhain EQN 13xx Datasheet – encoder resolution (29/12 bits), EnDat protocol version, 1 Vpp sin/cos with commutation. Available on the Heidenhain EQN 13xx product page.

Frequently Asked Questions