Table of Contents
Introduction
In industrial installations with PROFINET networks, a ring topology using MRP (Media Redundancy Protocol) is a common solution to ensure network redundancy. However, when devices inside that ring —such as Cisco switches— take longer to initialize than the PLC itself, a critical issue can occur: the Siemens CPU goes to STOP right after startup.
What is the Configuration Time in TIA Portal?
The Configuration Time (also referred to as Systemhochlaufzeit in German-language versions, or peripheral wait time) is a parameter found in the CPU hardware configuration inside TIA Portal. It defines the maximum time the CPU waits, after transitioning to RUN, for all PROFINET devices configured in the project to connect and respond correctly.
If any device has not completed its initialization before this timer expires, the CPU logs a PROFINET diagnostic error and, depending on the fault reaction settings, may go to STOP.
MRP Ring with a Cisco Switch
MRP (Media Redundancy Protocol — IEC 62439-2) is the Siemens standard protocol for creating redundant topologies in PROFINET networks. One node acts as the MRM (Media Redundancy Manager) —usually the CPU or a SCALANCE switch— blocking one of the ring ports to prevent loops. The remaining nodes operate as MRC (Media Redundancy Clients).
Solution: increase the Configuration Time
The solution is straightforward: increase the Configuration Time value in the CPU hardware configuration inside TIA Portal, giving slow devices (the Cisco switch) enough time to complete their initialisation before the CPU evaluates whether all IO Devices are available.
This adjustment does not negatively affect normal system operation. Under normal conditions (when all devices are already active), the CPU will detect the IO Devices well before the new timer expires, and the transition to RUN will occur in the usual time.
