Enabling SINAMICS S110 Traversing Block in STARTER: EPOS Setup

1. Problem Overview

The SINAMICS S110 is a single-axis servo converter family from Siemens used for positioning, speed, and torque control of synchronous and induction servomotors. The CU305 Control Unit integrates a Basic Positioner (EPOS) that supports three operating modes: jog, direct setpoint input / MDI (Manual Data Input), and traversing blocks (sometimes called "travel blocks" or "positioning blocks").

A common field issue reported by commissioning engineers is the following sequence:

• STARTER (or Startdrive) configuration wizard was completed and Basic Positioner was selected.
• Direct setpoint / MDI mode was tested and the "MDI enable" signal was confirmed — the green "active" indication in the control panel lights up.
• Traversing blocks were parameterized, but the green "block enabled" indication does not appear on the STARTER control panel or in the drive status word.
• Application requires 8 to 64 different fixed positioning targets (the S110 supports up to 64 traversing blocks per drive data set, p2617).

The root cause is almost always that the Basic Positioner technology option has not been activated in the active Drive Data Set (DDS), or that the control word bit that arms the traversing block interpreter (bit 0 / bit 4 of STW1 in PROFIdrive telegram mapping) is not being driven by the higher-level controller. This article walks through the exact configuration, parameter check, and verification sequence to bring the traversing block function online.

2. SINAMICS S110 Architecture and EPOS Operating Modes

The S110 firmware (FW 4.x and 5.x) splits the Basic Positioner functionality into several independent function blocks. The following diagram illustrates the functional layers and how the traversing block interpreter is selected:

To use traversing blocks the drive must be in EPOS operating mode (p1082 bit selection or via configuration wizard in STARTER), and the active DDS must contain the Basic Positioner technology option. Without this, p2617, p2625..p2659 remain hidden in the parameter list and the control word bits that select a block are ignored.

3. Root Cause Analysis — Why the Traversing Block "Enable" LED Stays Off

Based on the failure pattern (MDI active, traversing block not active), the cause lies in one of three layers:

4. Prerequisites

Before reconfiguring, confirm the following:

1. Drive firmware: S110 FW 5.2 SP3 or later is recommended for traversing blocks with the full 64-block range. Earlier FW 4.x versions support a subset (typically 16 blocks). The firmware version is read at p0018 / r0018 in STARTER.
2. Commissioning tool: STARTER V5.1 SP1 or higher, or TIA Portal Startdrive V15.1 and higher. The procedure below uses STARTER; Startdrive uses an equivalent wizard.
3. Drive / motor data: Motor identification, encoder calibration, and basic speed controller auto-tuning (p1900 / p1910) must be completed without faults.
4. Active DDS: Know which DDS is active at power-up (p1820 = 0..7) and which is the working DDS for the application.
5. Encoder configuration: The position actual value (r2521) must be stable; a missing or noisy encoder prevents traversing blocks from being released (drive signals F07490 "EPOS: traversing block not enabled").
6. PROFIdrive telegram: Telegram 7 or 110 is recommended for EPOS. Telegram 1/2/3/4 do not carry the dedicated EPOS bits, requiring BICO routing of p2617 and the control word bits from STW1.

5. Step-by-Step Configuration of the Traversing Block

5.1 Activate the Basic Positioner in the DDS

1. Open the S110 project in STARTER and double-click the CU305 drive object.
2. Click Configuration → DDS configuration in the navigation tree.
3. For the active DDS (e.g., DDS0), open the Function modules tab and enable the check box "Basic Positioner (EPOS)".
4. If your project uses multiple DDS (e.g., for gear-changeover), repeat the check in every DDS that must execute traversing blocks.
5. Click Apply and then Transfer to target (RAM).
6. Right-click the drive and select Copy RAM to ROM to persist the option change.
7. Perform a CU305 power-on restart (p0009 = 0; p0976 = 1 or mains off/on). The drive reboots with the new function module set.

5.2 Verify the Function Module Is Active

After the restart, enter the following online values in the expert list (right-click the drive → Expert list):

If r1082.7 is still 0 after the restart, the option list was not transferred. Re-do Transfer to target with Copy RAM to ROM enabled, and check the configuration file size (p0014 / r0014). A mismatch here is the single most common reason the green block-enable LED stays off.

5.3 Parameterize the Traversing Blocks

For the 12 blocks your application needs, fill in the parameter pairs shown below for each block number (n = 0..11):

The mode byte p2630 is bit-coded. A typical absolute positioning block uses 0x21 (bit 0 = absolute, bit 5 = identify response):

5.4 Configure the Active Block Selection (p2617)

The current block number is written to p2617 from one of three sources:

1. PROFIdrive STW2 bits 16..19 (binary selection, 0..15) when telegram 7 or 110 is used and BICO is at default.
2. PROFIdrive SZD (Signal Setpoint Direction) bits mapped via p2647, p2648, p2649, p2650 when using a binary-coded selector.
3. Direct BICO source from the PLC, e.g., p2617 = r2050.x for a 6-bit binary selector (up to 64 blocks).

For 12 blocks, the typical wiring from a Siemens SIMATIC S7 to the S110 uses STW2.16..STW2.19 (4 bits = 16 blocks) from a PROFINET telegram 110, and the PLC writes a 0..11 value to those bits just before toggling STW1.6 (activate traversing task).

5.5 Control and Status Word Sequence

The traversing block interpreter is armed and started by a specific bit pattern in STW1. The relevant bits for EPOS are:

The matching status bits in ZSW1 (r2089[0]) include:

The green "block enabled" LED in the STARTER control panel maps directly to ZSW1.10 (r2089.10) and the EPOS status word 1 bit 8 (r2684.8). If the LED is off, both of these bits are 0 — meaning either the block was never started (STW1.6 never toggled) or the interpreter rejected the block (check the block number range or the active DDS option).

6. PROFIdrive Telegram and BICO Wiring

For a clean PROFINET connection to a SIMATIC controller, the recommended telegram is 110 (which carries STW1/ZSW1, STW2/ZSW2, NSOLL_A, NIST_A, XERR, and the dedicated EPOS bits). Configure as follows:

1. In STARTER, navigate to Communication → Telegram configuration.
2. Set the standard telegram to Telegram 110.
3. Verify that the automatic BICO connection has linked p2617 to the bits of STW2 (r2094.16..r2094.21).
4. Save the project and re-download to the drive.

If the application must use telegram 1 (compact), manually BICO-route the control bits:

• p2647[0] = r2092.4 (reject traversing task from STW1.4)
• p2647[1] = r2092.5 (intermediate stop from STW1.5)
• p2647[2] = r2092.6 (activate traversing task from STW1.6)
• p2648[0..5] = r2094.16..r2094.21 (block number bits 0..5 from STW2)

7. Commissioning and Verification

1. Manual test in STARTER control panel:
   1. Open Commissioning → Control panel.
   2. Assume master control, enable the drive, write p2617 = 1 (block 1), then set the relevant STW1 bits via the buttons. Observe that the green "block enabled" indicator lights up and the drive moves to p2625[1].
   3. Repeat for blocks 2..11 to confirm all 12 blocks run.
2. Trace recording:
   1. Open the STARTER trace (Tools → Trace).
   2. Record r2521 (position actual value), r2556 (velocity actual), r2684 (EPOS status word 1), r2685 (EPOS status word 2), and r2089 (ZSW1).
   3. Verify that on the 0→1 edge of STW1.6, ZSW1.10 goes high within ≤ 4 ms and r2521 begins to follow the ramp defined by p2626..p2629.
3. Diagnostic LEDs on the CU305:
   • RDY (green) — steady when drive is in S4 (Operation) or S50 (Basic Operator Interface / manual mode).
   • BF (red, bus fault) — must be off; if on, PROFINET is not in cyclic data exchange and STW1.6 will not be processed.
   • SF (red) — group fault; read the buffer with r0945 / r0947.

8. Fault and Alarm Reference for EPOS

9. Troubleshooting Matrix

10. Common Pitfalls and Field-Proven Cautions

• Position scaling: One Length Unit (LU) is the base unit of the entire EPOS system. Define p2520 (reference distance) and p2521 (reference number of LU) such that one LU equals 1 µm or 1/1000 inch. Forgetting this means the drive will target the absolute raw LU count and overshoot or oscillate.
• Absolute vs relative: With bit 0 of p2630 = 0, the target position in p2625 is interpreted relative to the start position. For a 12-position rotary table, use bit 0 = 0 to keep the path consistent from any home position.
• Modulo correction: For axes that wrap around (rotary tables, turntables), enable modulo correction in p2576 and define p2577 (modulo range). Otherwise EPOS will treat the position as a single-turn linear axis and refuse to re-target after one full revolution.
• Backlash compensation: When mechanical backlash is significant, set p2603 (backlash compensation) and trigger a referencing run (active homing) before the first traversing block; otherwise the very first absolute target will be off by the backlash amount.
• Block transition events: For a 12-position pick-and-place, p2632 = 1 (continue with stop) and p2633 = next block number gives a deterministic block chain. For asynchronous operation, p2632 = 2 (continue flying) is faster but requires the next block to use the same direction.
• Active referencing: The very first traversing block after power-up will be rejected if the axis has not been referenced. Either set p2597 = 0 (no absolute encoder calibration required) only if the encoder supports it, or wire a home-position sequence (active homing via p2595) before the first block.
• STW2 bit order: Many PLC programmers assume the block number is bits 0..5. In the default BICO mapping, the block number is bits 16..21 of STW2, which arrive as a single 16-bit slot in the PZD. Verify the bit order in the SIMATIC HW configuration and the drive's r2094 mapping.
• Safety functions: If the S110 is wired into a SIMATIC F-CPU with PROFIsafe, the safety telegram (e.g., 30 or 901) must be active and the safety functions parameterized (STO, SS1, SS2) before the green EPOS enable can be raised.

11. Quick-Reference Parameter List

12. FAQ