1.3.2.4 Bus cycle time and data security
The communication via the CS31 bus is cyclic and controlled by the CS31 bus master.
Fig. 8: Format of request telegram of a CS31 bus master
In each cycle, the CS31 bus master successively polls all existing CS31 slaves at regular inter-
vals, performs a diagnosis on one of the existing CS31 slaves and sends a request to search for
added CS31 slaves. Thus, on one hand it is possible to maintain a continuous diagnosis of the
proper network function and on the other hand to take all the newly added CS31 slaves into
account.
Fig. 9: Format of response telegram of a CS31 slave
The CS31 slaves respond to the telegrams of the CS31 bus master with a response telegram
(see diagram above). The data are indicated in the documentation of the individual devices (e.g.
07AC91-AD2). The telegram is ignored when a CS31 slave or a CS31 bus master detects a
deviation between the received CRC and the self-calculated CRC. A CS31 bus error exists
when 10 faulty telegrams are issued successively.
The bus cycle time is composed of a base time, the bus transmission times of the data of the
individual CS31 slaves and the bus idle times between the individual telegrams.
During the base time, the CS31 bus master performs a diagnosis and searches for newly added
CS31 slaves. This time depends on the control system (PLC / central unit) and is partially con-
figurable:
● Devices 07KT94 and 07KT98: base time 2 ms
● Device 07KT94-ARC-AD: base time 10 ms *)
● Devices 07KT98-ARC-AD, 07KT98-ARC-DP-AD, 07KT98-ARC-ETH-AD, 07KT98-ETH-DP-
AD,
07KT98-ARC-ETH-DP-AD:
Base time 5 ms to 100 ms (configurable in Automation Builder, parameter "Min update
time")
*) The base time of device 07KT94-ARC-AD cannot be configured since the old programming
environment (907 PC 331) must be used.
The bus transmission times of the data of the individual CS31 slaves can be determined as fol-
lows:
● Duration for the transmission of 1 byte = (1/187.5 kBaud) x 8 = 43 µs
● Determine number of data bytes (sending + receiving) from existing documentation
● Add 3 bytes for the transmission of the address and CRCs
Per CS31 slave, approx. 0.5 ms can be assumed as bus idle time. The CS31 bus master needs
this time to process the data. This time depends on the computing power and on the implemen-
tation of the CS31 bus master. This time can vary between various firmware versions.
Fig. 10: Example bus cycle time
System data and CS31 bus system data > CS31 bus system data
2018/09/243ADR010122, 8, en_US14
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