Cause : Steady-state (static) 1 signal at the F-DI for safety-relevant acknowledgement comes when a logical 1 signal is present at the F-DI configured in p10106 for more than 10 seconds. If, at the F-DI no acknowledgment was performed for safe acknowledgment, then a steady-state logical and 0 signal must be present.

1. This avoids unintentional safety-relevant acknowledgement (or the "Internal Event Acknowledge" signal) if a wire breaks or one of the two digital inputs bounces.
2. Set the fail-safe digital input (F-DI) to a logical 0 signal (p10106).