Functionality/Feature	SERCOS I	SERCOS II	NEW SERCOS III
Date Implemented	1987	1999	2005
Over 500 standardized parameters, defining single and multi-axis motion control	Yes	Yes	Yes
Communication type	Serial	Serial	Serial
Physical media	Fiber optics	Fiber optics	Ethernet twisted-pair copper or fiber optics
Network topology	Ring	Ring	Line or ring
Transmission speed	2/4 Mbit/sec.	2/4/8/16 Mbit/sec.	100 Mbit/sec.
Operating modes	Velocity, current and position loops closed in the drive	Velocity, current and position loops closed in the drive	Velocity, current and position loops closed in the drive or position and velocity loops closed in the control, with only current loop closed in the drive.
Cycle times	Selectable from 62.5 µs and up.	Selectable from 62.5 µs and up.	Selectable from 31.25 µs and up.
Synchronization	Hardware synchronization	Hardware synchronization	Hardware synchronization
Message structures	Same	Same	Same
Multi-master communication and synchronization (C2C)	No	No	Yes
Slave-to-slave communication	No	No	Yes
Service channel	Yes	Yes	Yes
Optional IP channel	No	No	Yes
Jitter	<1us	<1us	<1us
Determinism	Yes	Yes	Yes
Number of masters	One per ring	One per ring	One per ring/line
Maximum number of nodes per network	254 per ring, multiple rings allowed.	254 per ring, multiple rings allowed.	254 per ring, multiple rings/lines allowed.
Physical & control standard	IEC 61491/EN61491	IEC 61491/EN61491
Support supervisory controls and additional I/O	Yes	Yes	Yes
Hot pluggable	No	No	Yes
Maximum cable length	Plastic – 40 m node-to-node; 10,000 m maximum ring length Glass – 800 m node to node; 200,000+ m max ring length	Plastic – 40 m node-to-node; 10,000 m maximum ring length Glass – 800 m node to node; 200,000+ m max ring length	Copper – 100 meters Fiber Optic –2000 meters
Communications modes	Cyclic – Deterministic time slice for managing realtime communications, speed depends on # of nodes on the ring. Cyclic data can be transmitted at rates as low as 62.5 us. Non-cyclic – Used for non-real-time data transfers such as status and diagnostic messages.	Cyclic – Deterministic time slice for managing real-time communications, speed depends on # of nodes on the ring. Cyclic data can be transmitted at rates as low as 62.5 us. Non-cyclic – Used for non-real-time data transfers such as status and diagnostic messages.	Cyclic – Deterministic time slice for managing real-time communications, speed depends on # of nodes on the ring. Cyclic data can be transmitted at rates as low as 31.25 us. Non-cyclic – Used for non-real-time data transfers such as status and diagnostic messages.