CANopen Safety and FSoE (Fail-Safe over EtherCAT) are both SIL 3 black-channel safety protocols governed by IEC 61784-3, so they are functionally equivalent in integrity. The decision is driven almost entirely by the transport you have already chosen: CANopen Safety runs on classical CAN (≤1 Mbit/s), FSoE on 100 Mbit/s EtherCAT. What differs is performance, footprint and ecosystem.
At a glance
| Criterion | CANopen Safety (SRDO) | FSoE (Safety over EtherCAT) |
|---|---|---|
| Transport | Classical CAN, ≤1 Mbit/s | EtherCAT, 100 Mbit/s full-duplex |
| Governing standard | EN 50325-5 (CiA 304) | ETG.5100 / IEC 61784-3-12 |
| Max integrity | SIL 3 / PL e | SIL 3 / PL e |
| Safety mechanism | SRDO: two bitwise-inverted CAN frames, CRC, SRVT time monitoring | FSoE frame in process data: 16-bit Connection ID, CRC, watchdog, state machine |
| Typical safety cycle | ~10–50 ms | ~1–4 ms |
| Master required | No — producer/consumer broadcast | Yes — MainInstance ↔ SubInstance |
| Hardware | Any CAN controller + transceiver | EtherCAT Slave Controller (ESC) |
Engineering detail
CANopen Safety’s core mechanism is the Safety-Related Data Object (SRDO): each is sent as two CAN frames with bitwise-inverted data and different identifiers, validated within a configured SR Validation Time (SRVT) and protected by a CRC. It is a producer/consumer broadcast model needing no central master, which suits distributed mobile-machinery safety, and it coexists with standard CANopen on the same bus.
FSoE embeds a compact safety container (Connection ID + CRC, ~6 bytes) inside the normal EtherCAT process image. Each connection runs a state machine and a watchdog that forces the safe state on any loss, delay, corruption or wrong Connection ID. Because EtherCAT provides sub-microsecond Distributed-Clock synchronisation, FSoE reaches 1–4 ms safety cycles — an order of magnitude faster than SRDO.
When to choose which
Choose CANopen Safety for cost-sensitive, distributed, lower-speed safety in mobile machines, off-highway and existing CAN networks. Choose FSoE when the machine already uses EtherCAT and you need fast safety reaction times for motion — multi-axis STO/SLS/SS1, robotics and machine tools.
The ISIT-Neperis stacks
ISIT-Neperis supplies pre-certified, SIL3-certifiable stacks for both: the CANopen Safety stack (EN 50325-5 / CiA 304) and the FSoE stack (IEC 61784-3-12), each delivered with the certification artefact pack your own assessment needs.