Siemens Simatic 6ES7 157-0AD81-0 A0 Series

Operation of the DP/PA Link and the Y Link
8-4
DP/PA Link and Y Link Bus Couplings
A5E00193841-011
8.2.2 Start-up behavior in redundant operation
LED displays
At the beginning of start-up, all LEDs of the IM 157 light up for approx. 1 second
for test purposes.