PROFINET IO update time and watchdog
A PROFINET IO device declares a communication failure after its update time multiplied by the accepted update cycles without IO data, which defaults to 3, so 6 ms at a 2 ms update time.
- Vendor or body
- PROFIBUS and PROFINET International (protocol); values as documented by PI and Siemens
- Model or version
- PROFINET IO real-time (RT) communication; Siemens STEP 7 (TIA Portal) settings
- Last verified
- Oct 5, 2026
- Sourced values
- 10
Values
| Parameter | Value | Condition |
|---|---|---|
| Watchdog time | Update time x cycles1 | Update time multiplied by the accepted update cycles without IO data. If the device gets no IO data within it, the device outputs substitute values and the controller reports a station failure. |
| Communication monitoring threshold | 3 cycles2 | Standard threshold. PI recommends keeping 3 and checking the response time if you change it. Vendors name this setting differently. |
| Error detection time at 2 ms update time | 6 ms2 | Threshold 3 (PI example). At a 4 ms update time the same threshold gives 12 ms. |
| Accepted update cycles without IO data | 33 | Default start value in the Siemens PN Watchdog Add-In for TIA Portal |
| Accepted update cycles range | 3 to 2553 | Values that can be set in the TIA Portal, as stated by Siemens |
| Update time range, all conformance classes | 1 to 512 ms2 | Basic function of every PROFINET conformance class |
| Update time range, Siemens example | 0.25 to 512 ms1 | Example CPU 1516-3 PN/DP with RT. Update times are reduction ratios of 1 to 512 of the send clock: 250 µs to 128 ms at a 250 µs send clock, up to 512 ms at a send clock of 1 ms or more. |
| Watchdog time with MRP rings | 200 ms3 | Siemens recommends a watchdog time of at least 200 ms in MRP ring configurations, since a ring is reconfigured within that time. Shorter values can work but are your responsibility. |
| Watchdog time on WLAN | Adjust as needed3 | Siemens notes that adjusting the watchdog time is advisable where WLAN is the communication medium. |
| Update time on wireless | May need increasing1 | With Industrial Wireless LAN you may have to increase the update time of wireless devices, because stations share the limited wireless bandwidth. |
Sources
- SIMATIC PROFINET with STEP 7 Function Manual (A5E03444486-AQ). Read Oct 5, 2026.
- PROFINET Design Guideline, Version 1.59 (Order No. 8.062). Read Oct 5, 2026.
- TIA Add-In: PN Watchdog (Entry ID 109769093, V1.4). Read Oct 5, 2026.
About this page
Built from 3 sources: 1 protocol owner or alliance and 2 vendor documents. Researched and drafted with AI assistance, then reviewed and approved by Ben Rutter on . How pages are made
- First published
- Last updated
Change history (1)
- First published
Cite this page
Plain
Ben Rutter. "PROFINET IO update time and watchdog." OT Wireless, published October 5, 2026. https://otwireless.com/requirements/profinet-io/
APA 7
Rutter, B. (2026, October 5). PROFINET IO update time and watchdog. OT Wireless. https://otwireless.com/requirements/profinet-io/
BibTeX
@misc{rutter2026profinetio,
author = {Rutter, Ben},
title = {{PROFINET IO update time and watchdog}},
year = {2026},
howpublished = {\url{https://otwireless.com/requirements/profinet-io/}},
organization = {OT Wireless},
}