Ethernet / VARAN
In the Ethernet standard IEEE 802.3 data collisions cause irregular delays in data transfer. In order to achieve real-time performance, Industrial Ethernet protocols employ special preventive measures to avoid such collisions.
For hard real-time, signal transmission times must stick exactly to a given time frame, or else they will trigger a failure signal. For soft real-time, some deviation within a limited span of time is tolerable. While cycle times of up to several hundred milliseconds may be good enough for soft real-time applications, e.g. for temperature monitoring, digital control systems or Motion Control applications often require cycle times below one millisecond.
When selecting the right bus system for machine automation, reliability plays a central role in addition to the speed. Based on globally proven Ethernet physics, the hard real-time at the lowest cycle times and maximum data security is provided. Robust, error-tolerant performance in raw industrial environments is also an important performance characteristic of a modern bus system. As a real-time Ethernet bus system, the VARAN bus meets these requirements and offers much more.
The company "Sigmatek" has developed in 1994 a real-time bus system for connecting the I / O modules of in that time introduced product series DIAS (DIAS-BUS). VARAN is the evolution of the DIAS bus based on Ethernet. In the year 2006 the activities relating to disclosure and standardization of the system were transferred to VARAN BUS USER ORGANIZATION (VNO).
The VARAN bus is based on standard Ethernet technology. The protocol is implemented completely in the hardware, whereby the burden on the control CPU is reduced. Instead of standard Ethernet frames, smaller data packets are used with the VARAN bus, guaranteeing the highest possible resistance to disruptions. The immediate repetition of unacknowledged messages within a bus cycle is one of the most important advantages, which characterize the VARAN bus as a future-oriented bus system.
By using the Manager-Client principle, collisions are avoided. The VARAN bus provides highest speed, shortest cycle time and minimum synchronicity jitter. In addition, it offers the unique possibility of asynchronous direct access.
Data packets are repeated within the cycle until a valid acknowledgment is received. Therefore, the validity of all data is guaranteed at the end of each cycle. This permanent testing of data validity, even for bus cycle times less than 100 µs, is only possible through use of the small VARAN data frames (1 – 128 bytes). Due to the flexible network topology, star-, line- and tree-topologies can be combined as desired. Another advantage is the easy implementation of existing CANopen® protocols.
The VARAN bus is an open standard and manufacturer-independent.