Resolving TIA Portal 'No Update Time Calculated' for V90 PROFINET

1. Problem Overview

A typical commissioning sequence with a SIMATIC S7-1500 CPU 1512C-1 PN, a SINAMICS V90 PROFINET servo drive, and a SCALANCE X208 managed switch fails in TIA Portal with the compile-time message:

No update time can be calculated for IO device <Servo_Device_Name>.

The same project often produces a second, related diagnostic:

Isochronous mode is enabled on device "Servo" although IRT (high performance) is not set.

Both messages originate from TIA Portal's PROFINET IO planner when it cannot reconcile the requested transmission class (RT or IRT), the selected PROFIdrive telegram, the isochronous mode setting on the drive, and the switching capability of the intermediate SCALANCE. The error blocks download to the PLC, prevents the device from going online, and prevents port-interconnect (the red "go to" line) from being cleared.

2. Affected Components and Typical Topology

The user's fault topology is therefore:

PLC 1512C-1 PN  ---[ PN port X1 ]--- SCALANCE X208 ---[ port ]--- SINAMICS V90 PN
      (IRT master)               (RT switch only)              (IRT-capable device)

3. Root Cause Analysis

3.1 Why TIA Portal Refuses to Calculate an Update Time

When the controller's port is configured for IRT, TIA Portal walks the topology and verifies that every switch on the path is on the official "PROFINET IO IRT (high performance)" switch list. If any switch is only "PROFINET IO device" certified (RT only), the planner cannot assign a deterministic send clock and aborts with the diagnostic shown above. The SCALANCE X208, despite being a PROFINET-conformant managed switch, is not on the IRT switch whitelist. It supports only PROFINET RT and standard Ethernet.

Per the official SCALANCE X-200 product manual (Siemens AG, edition 2023-09), the X208 family is described as "PROFINET device, RT class 1" and is explicitly not approved for IRT (high performance). The SCALANCE XC208 (compact) variant shares this restriction.

3.2 The Companion Isochronous-Mode Error

PROFINET isochronous mode (drive synchronous, jitter < 1 µs) is only available on top of IRT (high performance). When the V90 is configured with:

• Telegram 105 (SIEMENS-specific, 16-word PZD with DSC and torque data), or
• Drive-side "Activate isochronous mode" = checked in the V90 parameter p0922 / PROFIdrive tab

the controller demands IRT. Because the X208 cannot forward IRT frames, TIA Portal surfaces the message:

Isochronous mode is enabled on device "<name>" although IRT (high performance) is not set.

3.3 Why the "Go to" Button Cannot Clear the Line

The red line in the topology editor is a hard constraint from the PROFINET IO planner; it is not a soft wiring hint. Until the planner can find an update time, the interconnect is locked and right-click actions on the line are disabled. The compiler refuses to produce system data (SDB) until the constraint is satisfied.

4. Quick Diagnostic Procedure

1. Open Devices & Networks and select the SINAMICS V90 device.
2. In the inspector, open Properties > PROFINET interface > Advanced options > Real-time settings and note the Transmission mode: RT or IRT.
3. Open Properties > PROFINET interface > Telegram configuration and read the active Standard telegram (1, 2, 3, 5, 102, 105, ...).
4. Click each port of the SCALANCE X208 (or XC208) and inspect Properties > Port options > PROFINET IO. If the port option "IRT forwarding" is absent or grayed out, the switch cannot carry IRT.
5. Right-click the PROFINET IO system → PROFINET IO topology and verify the cable lengths match the installed cabling (TIA Portal needs accurate cable lengths to compute the line delay).
6. Compile the project (Compile > Hardware (rebuild all)) and read the messages in the Inspector window under Info > Compile. The compile log names the offending IO device.

5. Resolution Paths

Four mutually exclusive paths are valid. Pick the one that matches your application requirement.

5.1 Path A - Keep X208, Switch V90 to RT + Telegram 3

When to use: No isochronous motion required, standard positioning or speed control with cycle times > 1 ms.

1. Open the V90 device > Properties > PROFINET interface > Real-time settings.
2. Set Transmission mode = RT.
3. Open Telegram configuration, remove Telegram 105, and add Standard Telegram 3 (8 PZD, speed setpoint / actual with 32-bit resolution and 2 trace channels).
4. On the drive side, clear Activate isochronous mode in the PROFIdrive parameter screen.
5. Recompile. The update time error should disappear; TIA Portal computes the send clock automatically (default 1 ms for RT on a 1512C).
6. If the application needs torque control, use SIEMENS Telegram 102 (10 PZD) instead of 105; it is also RT-compatible.

5.2 Path B - Replace the X208 with an IRT-Capable SCALANCE

When to use: Drive synchronization or DSC is mandatory (high-dynamic camming, electronic gearing, print-mark registration, etc.).

1. Delete the SCALANCE X208 from the device configuration.
2. Insert a SCALANCE X204 IRT (6GK5204-0BA00-2AB2) or, for more ports, SCALANCE X206-1 IRT / X212-2 IRT.
3. Wire the topology in the topology editor: PLC port X1.P1 → X204 IRT port 1, X204 IRT port 2 → V90 port 1.
4. Set the Transmission mode on the V90 back to IRT and re-add Telegram 105.
5. In the V90 inspector, open PROFINET interface > Advanced > Port interconnection and confirm the "Used as IRT high-performance port" checkbox appears on each linked port.
6. Compile. The planner should now show a valid send clock of 250 µs, 500 µs, 1 ms, or 2 ms, depending on the cycle selected in the PROFINET IO system.

For larger machine networks, a SCALANCE XC216-4C IRT (6GK5216-4BS00-2AB2) or SCALANCE XF204 IRT can be used; all SCALANCE "IRT" suffixed variants are IRT (high performance) capable.

5.3 Path C - Connect the V90 Directly to the CPU

When to use: Single-axis machine, no additional distributed I/O, and the S7-1500 has a free PROFINET port.

1. Delete the SCALANCE from the project.
2. Drag a direct PROFINET "subnet" connection between the CPU 1512C-1 PN port X1.P1 and the V90 PROFINET port.
3. Configure IRT and Telegram 105 as in Path B.
4. Compile and download.

5.4 Path D - Replace V90 with SINAMICS S210

When to use: Modern machine design where you want to keep the existing SCALANCE XC208 and move to a newer servo platform. The S210 is built natively for PROFINET IRT and supports Telegram 105 over RT as well, which broadens your switch options.

1. Delete the V90 from the project.
2. From the catalog, insert the SINAMICS S210 PROFINET variant (for example 6SL5310-1BB10-1DF0 control unit with 1FK2 / 1FT2 motor).
3. Configure Telegram 3 for RT operation with the existing XC208, or Telegram 105 for IRT with an IRT switch.
4. Compile. Telegram 105 is now valid over IRT, but it is also acceptable to run the S210 with Telegram 3 over RT if jitter is not critical.

6. Telegram Compatibility Reference

Source: Siemens SINAMICS V90 PROFINET Function Manual, 05/2023 edition; SINAMICS S210 System Manual, 06/2024 edition.

7. SCALANCE Switch Capability Matrix

8. Detailed TIA Portal Configuration Steps (Path A Worked Example)

1. Open the project in TIA Portal V18 or later (the user's compile-time check applies to all V16+ releases; V20 is current).
2. In the project tree, double-click Devices & Networks.
3. Click the SINAMICS V90 device. The Inspector opens on the right.
4. Navigate to Properties > PROFINET interface > Real-time settings:

5. Open Properties > Telegram configuration. The default in many project wizards is Telegram 105. Replace it with Standard Telegram 3.
6. Open Properties > PROFINET interface > Advanced > Isochronous mode and uncheck Activate isochronous mode.
7. Click Compile > Hardware (rebuild all).
8. The compile log should now show Update time 1.000 ms for device Servo and no error.
9. Right-click the CPU and choose Download to device > Hardware and software.
10. Open the online V90 diagnostic view; confirm Telegram 3 is active and that the controller is sending process data without F01910.

9. Verification and Commissioning Checklist

For an S7-1200 target, the equivalent steps and parameters are described in docs.tia.siemens.cloud - Configuring the IO cycle time (S7-1200).

10. Common Field Pitfalls

• Forgot to clear "Isochronous mode" on the drive: the drive keeps p8811 / isochronous settings in RAM after the PLC changes its telegram; do a power cycle or save to ROM (p0977 = 1) after reconfiguring.
• Mixed IRT and RT in the same PROFINET IO system: an IO controller can run a mixed system but the IRT devices must be on a contiguous IRT-capable segment. Putting a V90 (IRT) on an X208 (RT) segment forces the controller to demote the device to RT, which then collides with Telegram 105.
• Topology cable lengths set to 0 m: TIA Portal uses the cable lengths to compute line delay; if left at zero the planner may still pass but real-world jitter becomes unpredictable. Enter measured lengths.
• Port interconnect in topology view is missing: in IRT projects, you must define the port-to-port neighbors in the topology editor, not just connect them in the network view.
• Firmware too old: V90 PN firmware < 1.04 may not correctly handle Telegram 3 with 32-bit speed values; upgrade to the current FW package available in the Siemens online support.
• CP 1542-1 used by mistake: this communication processor supports PROFINET RT only. Even though it has PROFINET in its name, it cannot forward IRT.

11. Migration Tip: V90 to S210

If your machine roadmap includes a switch swap but you want to stay with IRT-grade motion, the SINAMICS S210 paired with a SCALANCE XC216-4C IRT is the cleanest Siemens-native migration. Telegram 105 and DSC continue to work, but you also gain one-button auto-tuning, integrated safety (PROFIsafe over PROFINET), and a safety-rated encoder interface. The S210 supports the same PROFIdrive state machine and the same TIA Portal libraries (LAxisBasic / SINAMICS S210 blocks), which keeps the PLC code changes minimal.

12. Frequently Asked Questions