Lenze I/O system 1000 System Manual - Manual (Page 389)

PROFIBUS communication
Communication
Bus access
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389 EDSIO1000 EN 7.0
9.3 Communication
9.3.1 Bus access
The transmission protocol offers two bus access procedures.
Master
« Master
The master communication is also referred to as token passing procedure. The token
passing procedure makes sure that the bus access authorisation is assigned. The bus access
authorisation is given by means of a "token". The token is a special telegram transmitted
via the bus.
If a master has a token, it can communicate with all of the other bus nodes. The token hold
time is defined during system configuration. Once the token hold time has elapsed, the
token is passed on to the next master which is then in possession of the bus access
authorisation and can communicate with all of the other nodes.
The data transfer between the master and the slaves assigned to it is automatically
controlled by the master and takes place in a fixed and recurring sequence. The slaves are
assigned to a master during configuration. In addition, it can be defined which slaves
participate in the cyclic process data transfer.
Master
« Slave
Before master and slave can communicate, the configuration and the parameter setting
are checked for errors after startup.
The following are checked: type, format information, length information and the number
of inputs and outputs.
If the parameters are valid, the slave changes over to the DataExchange (DE) state. The
master can now transmit output data to the slave and receive the current input data from
the slave.
While the process data transfer is in progress, the master can transmit new parameter data
to the slave.