Configuring SIMOTION D425 Homing Output Cam and I/O Address

Overview

The SIMOTION D425-2 DP/PN (Siemens part number 6AU1425-2AD00-0AA0) integrates a SIMOTION motion controller and a SINAMICS S120 Control Unit (CU320-2) on a single module. This BASIC-performance motion controller exposes 12 dedicated digital inputs and 16 bidirectional DI/DO onboard, plus 4 DRIVE-CLiQ ports, 2 PROFIBUS interfaces, 3 PROFINET ports, 2 Ethernet, 2 USB, and 1 option slot.

Configuring a homing sequence on this controller requires three coordinated steps:

1. Select the homing mode (Homing output cam and encoder zero mark) in the SIMOTION SCOUT axis configuration.
2. Map the physical homing cam sensor to a logical address on the I/O area of the SIMOTION/CU.
3. Wire the onboard DI/DO of the D425-2 into the configured logical address through the SINAMICS telegram and BICO configuration (drive parameter p0922, parameter number P390 for SIEMENS telegram 390, and reset to 999 to surface the BICO interconnections).

This article walks through each step, derives the logical address byte/bit offset, and adds an MCC program block to acknowledge technology-object (TO) alarms from a pushbutton input.

Prerequisites

SIMOTION D425-2 Onboard I/O Architecture

The D425-2 carries the digital I/O on the integrated SINAMICS CU320-2. The I/O appear in the PROFIdrive process data word (PZD) area of the message frame, not as direct SIMOTION I/O. The mapping follows the rules of SINAMICS S120.

Connector Layout (X122 / X132)

Homing Mode Selection in SCOUT

1. Open the SIMOTION project in SCOUT and navigate to the Axes → <AxisName> → Homing configuration dialog.
2. Set the homing mode to Homing output cam and encoder zero mark. This forces the axis to move toward the cam, decelerate on the cam edge, search the next encoder zero mark, and latch the position.
3. Two parameter fields appear under the mode list:
   • Log. address of homing output — byte offset of the I/O byte that contains the cam bit.
   • Bit number — bit position inside that byte (0…7).

The combination of byte address + bit number must point to the actual physical input on the D425-2 that the cam is wired to.

Logical Address Calculation

The SIMOTION I/O area used by the homing configuration is the same I/O area assigned to the SINAMICS Control Unit during PROFIBUS / PROFINET configuration. The D425-2’s onboard DI/DO appear inside the message frame (telegram) of the integrated CU320-2.

Step 1 — Determine the CU Start Address

Open the device configuration of the CU320-2 in SCOUT. In the Properties → PROFINET interface / PROFIBUS dialog, note the input address and output address of the message frame. Example for a default project:

Input  start address  : 256 (decimal) = 0x100
Output start address  : 256 (decimal) = 0x100

Step 2 — Apply the DI/DO Offset

Per Siemens SINAMICS S120 / SIMOTION D4x5 documentation, the first 8 onboard DI (DI0…DI7) occupy the low byte of the message frame, and DI/DO8…DI/DO15 occupy offset +3 (the third byte). The mapping is therefore:

Step 3 — Compute the Log Address

For a project where the CU start input address is 256 and the homing cam is wired to DI/DO11:

Log. address of homing output = 256 + 3 = 259 (decimal)
Bit number                      = 3

Enter these two values into the SCOUT homing dialog. Save and download to the D425-2 (target system → download → selected target devices).

Enabling the BICO Table on the CU (p0922 / Parameter 390)

By default, the onboard DI of the SINAMICS CU320-2 are not directly mapped to free I/O for the SIMOTION homing mechanism; they are wired to internal CU status words. To expose the DI/DO bytes as freely-readable process data, the SINAMICS telegram must be extended or changed.

1. Open the CU320-2 expert list (or SCOUT drive configuration → Properties → Message frame).
2. Set p0922 = 390 (SIEMENS-specific telegram 390, which exposes the onboard I/O in PZD3). For applications using only PROFIdrive standard telegrams, an alternative is to select free telegram configuration and append DI/DO as PZD words. Telegram 390 is supported on firmware V4.6 and later.
3. After entering p0922 = 390, change the parameter once to p0922 = 999 (initial state / free configuration) and re-acknowledge with p0977 = 1. This forces the drive to release the BICO interconnections for the onboard DI/DO, exposing them as free status bits. Re-enter p0922 = 390 afterwards.
4. Carry out RAM-to-ROM (copy RAM to ROM, p0977 = 1) and a POWER ON for the changes to become active.

Linking the Onboard DI/DO to the Homing Logical Address

Once telegram 390 is active, the onboard DI/DO appear as process data bits. Two wirings remain:

1. The onboard terminal bit (DI/DO9…15) is already physically wired to the message frame PZD3 at the byte offset listed above. No additional BICO wiring is required for the input direction.
2. The SIMOTION homing configuration accesses the input through the SIMOTION I/O address space. Because the CU start address (e.g., 256) is configured as the input start in the SIMOTION device configuration, the homing logic reading byte 259 bit 3 correctly samples DI/DO11.

If the homing cam is connected to a different physical input (e.g., DI0 on X122.1), the corresponding offset is different. With CU start = 256, DI0 maps to byte 256, bit 0. Configure SCOUT accordingly:

Log. address of homing output = 256
Bit number                      = 0

Visualizing the Mapping

The following inline SVG illustrates the logical address chain from the physical terminal to the homing algorithm:

Acknowledging Technology-Object Alarms via MCC

The Acknowledge technology object alarms MCC command (German: Quittieren Technologieobjektalarme) is part of the SIMOTION MCC library and is bound to the technology object (TO) of the axis. To trigger it from a pushbutton wired to an onboard DI:

Program Structure (MCC chart AxisControl)

// Declare I/O variables
VAR_GLOBAL
    bAckPushbutton : BOOL;    // Mapped from input, e.g., CU_start + 3, bit 4 (DI/DO12)
    bRisingEdge    : BOOL;
END_VAR

Add the following MCC commands in a task of execution level IPO / IPO_2 or higher (e.g., BackgroundTask for non-time-critical acknowledge):

1. Edge detection on the pushbutton: _rising(bAckPushbutton, bRisingEdge) or use the MCC Detect rising edge command.
2. Acknowledge TO alarms command (chart menu → Insert → Single commands → Acknowledge technology object alarms):

// MCC pseudo-code
gAxisName.AcknowledgeTechnologyObjectAlarms(    // Axis TO identifier
    Execute := bRisingEdge,
    CommandId := 1
);

Why Compilation Errors Occur

Compilation errors at this point usually mean one of the following:

Alternative: ST Implementation

When the MCC command is unavailable in the library, use a Structured Text equivalent inside an MCC ST source file block:

IF bRisingEdge THEN
    _acknowledgeAlarms(axis := Axis_1,   // TO instance name
                       followUpMode := ALL);
    bRisingEdge := FALSE;
END_IF;

The system function _acknowledgeAlarms is declared in the SIMOTION system library SIMOTION System Functions / Basic.

Verification and Commissioning

1. Online check of the address: in SCOUT, connect to the D425-2, open Commissioning → Axis → Homing, and use the online Test cam function. The displayed logical address must match what is wired.
2. Trace the bit: enable the SCOUT trace on the homing status word and trigger the cam manually. Verify the bit toggles in the trace window.
3. Execute a homing run in JOG: jog the axis toward the cam at low velocity (v_jog_home = 10% v_max). The axis should decelerate on the cam edge and latch at the first zero mark after the cam rising edge.
4. Check error reactions: temporarily disconnect the cam wire. The axis should report F07452 / F31118 (cam missing) and stop with a controlled fault. Reconnect and use the MCC acknowledge to clear.

Troubleshooting Matrix

Field-Proven Caveats

• The byte/bit notation in SCOUT is byte.bit with the bit numbered from 0, not 1. Some SIMOTION dialogs display the bit number as 1-based. Always cross-check by viewing the actual SCOUT address field, which is always 0-based.
• CU320-2 input filter (p0401.0…7) defaults to 11 ms. For high-speed homing cam applications (v_home > 1 m/s), reduce to 1 ms or 0.5 ms to avoid missing the cam edge.
• If multiple axes share the same CU320-2 telegram, the onboard DI/DO of the D425-2 are not available to other axes via that telegram. Use a separate PROFIsafe or PROFINET I/O slice for shared sensors.
• Parameter p0977 = 1 is the SINAMICS “copy RAM to ROM and warm restart” command. Use this once after changing telegram settings, not on every boot.
• The MCC Acknowledge technology object alarms command clears faults on the bound TO only. Drive-level faults on the SINAMICS side (e.g., F30001) must be acknowledged through the drive object (CU320-2) using _acknowledgeAlarms with the drive DO instance, or via p3981 on the drive side.