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

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.

Hello,

Have you already installed the latest Service Pack 4 and Hotfix 19 for V5.5?

Best regards