Step 7 PROFIBUS Watchdog Timeout ONLY on Power-Up (Siemens ET200S) - CPU Enters STOP Mode

[Davin]

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Hello esteemed experts and colleagues,
I am working with a Siemens S7 automation system and I am currently facing a critical and persistent Watchdog Timeout issue on our PROFIBUS DP network.

1. Hardware Overview​

• Master: Siemens S7 CPU [Specify your CPU model, eg, 315-2 DP]
• Slave: Siemens ET200S Distributed I/O (Interface Module: [Specify IM model, eg, IM 151-1])
• Software: [Specify software version, eg, Step 7 V5.5 ]

• 2. Detailed problem description​

  The fault is highly specific and predictable:
  
  1. On Initial Power-Up: When the system powers up, the CPU immediately detects a fault and transitions to STOP mode .
  2. Diagnostics Buffer: The Diagnostics Buffer confirms a Watchdog Timeout for the specific ET200S PROFIBUS address [Specify DP Address, eg, Address 3]. This indicates the ET200S failed to respond in time during the initial communication handshake.
  3. Manual Recovery: The issue is completely resolved when the CPU is manually cycled from STOP to RUN . The communication is established instantly, and the system runs error-free until the next power cycle.

 

[A3Q]

Hi,
you can set the amount of time the CPU waits until all slaves respond at startup. If this time is exceeded, the response depends on the “Target/Actual Expansion” setting.

CPU properties > startup tab: increase the monitoring time. Should be something like “Completion notification".

PS: I don't have an English version, so the wording may differ slightly.

 

[vollmi]

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1. On Initial Power-Up: When the system powers up, the CPU immediately detects a fault and transitions to STOP mode .
2. Diagnostics Buffer: The Diagnostics Buffer confirms a Watchdog Timeout for the specific ET200S PROFIBUS address [Specify DP Address, eg, Address 3]. This indicates the ET200S failed to respond in time during the initial communication handshake.
3. Manual Recovery: The issue is completely resolved when the CPU is manually cycled from STOP to RUN . The communication is established instantly, and the system runs error-free until the next power cycle.

Is the DP-Remote at the Same Powersupply as the CPU? Then perhaps, the Remote boots up to slow. but is there at the Run-Stop-Run Cycle.
You can either load the according OB to avoid this (But thenthe cpu will run without the DP-Remote if it fails, you have to take care of that).

The OBs would be O121, OB82 and i think OB86.
or you rise the time for the ["Finished" message from Module] in the Startup Monitoring of the CPU