BECKHOFF BK2000 - Manual (Page 21)

Beckhoff-Lightbus coupler BK2000
BK2000 21
The Int command can also be triggered by a broadcast telegram. The
master can therefore trigger a simultaneous interrupt in all stations. The
control byte in the telegram is written with 0Bhex to use a broadcast. The
telegram address during the broadcast telegram is "255".
System behavior The system behavior of the Beckhoff-Lightbus was standardized to ensure
interchangeability of hardware. It is essentially defined by the operating
states of the Beckhoff-Lightbus modules belonging to previous series. The
following two main states are distinguished:
Modes
Stop No data communication takes place between the master and the
slaves. The bus coupler only addresses the bus terminals once
after power-on. It then does not address them again (none of the
I/O LEDs is lit).
Operation The master is in the data transfer phase. Within the scope of
cyclic data communication, the inputs of the slaves are read and
the output information is transferred to the slaves (the green
I/O LED is lit).
The master cyclically sends telegrams to all slaves in the ring at an interval
that depends on the size of the system and the parametrization. A slave
demands a valid telegram every 23 ms. This telegram need not necessarily
be addressed to a slave. The slave assumes an error state if it does not
receive it regularly. The green CYC LED no longer lights up and the red
ERROR LED additionally indicates an errored telegram. The system
reaction after the occurrence of an error in the master's data transfer
phase, e.g. failure of a slave, is defined by the fixed "watchdog timer"
operating parameter. If its time period has been exceeded, the slave
switches the outputs to the safe state. As soon as a slave is no longer
ready for user information data transfers, or transfer from the master has
been interrupted or is disturbed, after a slave has switched to the STOP
state the other slaves also directly assume this STOP state.
Data communication
between the slaves Data communication between the master and the slaves is handled auto-
matically by the master in a defined, recurring order. When considering the
bus system, the user defines the affiliation of a slave to diverse priority
levels, "CDLs", in the master. In doing so, it is possible to use one slave
simultaneously in several "CDLs". In one bus coupler, different sub-areas
of the data can also be queried in different "CDLs".
Data communication between the master and the slaves is broken down
into parametrization, configuration and data transfer phases. Before a
slave is included in the data transfer phase, the master checks in the
parametrization and configuration phase whether the configured nominal
configuration agrees with the actual hardware configuration and the
arrangement in the ring. During this check, the device type, the format and
length information and the number of inputs and outputs must agree. This
provides the user with protection against parametrization errors. In addition
to user information data transfer, which is realized automatically by the
master, it is possible to send new parametrization data to the Beckhoff-
Lightbus coupler at the user's request.
The medium: connectors
and cables The Beckhoff-Lightbus exclusively uses fiber-optic cable to transfer its
data. Two different cable types, plastic and fiber optic cables, are available
in a standard sheath and a protective sheath version.