Siemens SICAM AK Manual page 22

Redundancy via SCA-RS
Example for CPU redundancy:
The FUD runs for instance on both C-CPUs of the AU. The synchronization mode is HSL with
singular Ax-PEs (here an example for CPU redundancy).
A detailed system overview can be found in section 1.2.1.1,
electrically connected.
Example for AU redundancy:
The synchronization mode is Sync. via communication, if CAEx plus is used on both
redundancy BSEs.
If the distance between both AUs is more than 200 m, in all cases the redundancy
synchronization must take place over a separate fast data connection. In this case no singular
Ax-PEs are permitted.
22
SICAM AK - SICAM AK PE,
Unrestricted SICAM RTUs, SICAM AK Redundancy
Edition 10.2016, DC2-026-2.07