HSR applies the PRP principle of parallel operation to a single

ring. For each message sent, the node sends two frames, one

through each port. Both frames circulate in opposite directions

over the ring. Every node forwards the frames it receives from

one port to another to reach the next node. When the

originating sender node receives the frame it sent, the sender

node discards the frame to avoid loops. The HSR ring supports

the connection of up to 30 relays. If more than 30 relays are to

be connected, it is recommended to split the network into

several rings to guarantee the performance for real-time

applications.

The relay can be connected to Ethernet-based communication

systems in a station bus using the RJ-45 connector (100Base

TX) or the multimode fiber optic LC connector (100Base-FX). A

dedicated protection communication port uses a pluggable

multimode or single-mode fiber optic LC connector (100Base

FX). If connection to a serial bus is required, the RS-485 or

fiber-optic serial communication ports can be used.

Modbus implementation supports RTU, ASCII and TCP modes.

Besides standard Modbus functionality, the relay supports

retrieval of time-stamped events, changing the active setting

group and uploading of the latest fault records. If a Modbus

TCP connection is used, five clients can be connected to the

relay simultaneously. Further, Modbus serial and Modbus TCP

can be used in parallel, and, if required, both IEC 61850 and

Modbus can be run simultaneously.