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 supports Profibus DPV1 with support of SPA-ZC 302

Profibus adapter. If Profibus is required, the relay must be

ordered with Modbus serial options. Modbus implementation

includes SPA protocol emulation functionality. This functionality

enables connection to SPA-ZC 302.

When the relay uses the RS-485 bus for the serial

communication, both two- and four-wire connections are

supported. Termination and pull-up/down resistors can be

configured with DIP switch on the communication card so that

external resistors are not needed.