Time synchronization, Transmission reliability

This catalog is out of date, see note on page 2

Mode of operation

Redundant operation mode, transmission reliability, synchronization

Redundant operation mode

The CS 275 bus system can be redundant in order to increase the availability. The interface modules for the local bus are al- ready designed for a redundant local bus line. A bus converter UI and a connector board AF are required for connection of a redundant remote bus per remote bus cable. Different remote bus cable lengths are permissible between bus A and the re- dundant bus B.

The bus system is started up on bus A. Besides this, no prefer- ence is given to either bus. The bus system carries out a cyclic test to see whether a changeover criterion is satisfied. An auto- matic changeover is carried out if this is the case.

Changeover criteria

An image of the local bus is generated through each bus line approx. every 750 ms. If the image of the passive bus con- tains more entries than that of the active bus, the system switches to the passive bus.

If the images on the two bus lines are the same, but the mas- ter detects a transfer request on the passive bus, a change- over also takes place to the passive bus. A slave sends trans- fer requests on the passive bus if transfers are no longer possible for it on the active bus.

If the current master fails because of a fault, the slave with the smallest participant address assumes the master function on the previously passive bus (if one exists).

The bus changeover is signalled to all bus participants.

Time synchronization

The real-time clocks of the particular TELEPERM M subsystems are synchronized by signals from an OS operation and monitor- ing system. This can be synchronized by a radio clock (DCF 77 radio transmitter) or a standard clock.

The subscribers on the CS 275 bus system must be synchro- nized with high accuracy. Because of it, the transit time of the synchronization message is corrected within the milliseconds range by the internal buffers of the local bus interface modules of the automation systems and programmable controllers or by bus couplers.

Date and time transmission program

Remote bus 1

Time receive memory

Intermediate time counter ' t (ms)

Transmission buffer

Remote bus 2

Fig. 2/3 Time generation, time synchronization

Transmission reliability

In addition to data security of the transmission method, the fol- lowing measures ensure high transmission reliability in the physical transmission path:

Noise immunity to IEC 255-4 Triple screened cable, redundant