All Data valid at the end of the cycle
For industrial applications, the highest data security, as well as availability are deciding factors. For this reason, particular attention was given to data validity at the end of every bus cycle during the development of VARAN. Each manager command is immediately confirmed by the client.
Through the use of the short VARAN data frames (1-128 bytes), the permanent testing of data validity – even with bus cycle times under 100 µs – is made possible.
If the client does not answer within the defined timeout period, the data packet is repeated in the same bus cycle until a valid answer is returned. This process guarantees the validity of all data at the end of a bus cycle.
Through their low payloads (1-128 bytes) and data overhead, the VARAN data frames are essentially more resistant to disruptions than large standard Ethernet packets in other bus systems with lengths up to 1,500 bytes.
The probability of a disruption is significantly lower for small frames and in the event of an error, only a small data packet with a max. payload of 128 bytes must be resent.
Data Handling: All in good time.
The VARAN bus protocol distinguishes between three different tasks, as well as asynchronous direct access to prioritize tasks in the bus system. After the global SYNC command in the isochronous task (ISO), the real-time process data as well as the asynchronous data objects (ASYN) are transmitted. At the end, Ethernet packets and service data are sent in the administration task.
Asynchronous direct access
VARAN enables asynchronous direct access to bus participants at any time: The manager can interrupt active communication for up to 25 µs and send process data to the VARAN clients between the cycle times. Data can therefore be sent exactly at the calculated time and does not have to wait for the next cycle.