PROFIBUS
BC3150
81
Version: 2.1.0
Data traffic between the DPM1 and the DP slaves
The data traffic between the DPM1 and the DP slaves that have been assigned to it is automatically
executed by the DPM1 in a specified, continuously repeated sequence. The user specifies the assignment of
a DP slave to the DPM1 when the bus system's project is being planned. Those DP slaves that are included
in or excluded from the cyclic user data traffic are also defined.
The data traffic between the DPM1 and the DP slaves is divided into the parameterization, configuration and
data transfer phases.
Before a DP slave is included in the data transfer phase, the DPM1 checks, in the parameterization and
configuration phase, whether the theoretical configuration that has been planned agrees with the actual
configuration of devices. The check requires the device type, the format and length information, as well as
the number of inputs and outputs, to be in agreement. The user is thus provided with reliable protection
against errors in parameterization. In addition to the transfer of user data, which is automatically carried out
by the DPM1, it is possible to send new parameterization data to the DP slaves at the user's request.
Protection mechanisms
In the context of decentralized peripherals it is necessary, for reasons of safety and reliability, for the system
to be given extremely effective functions to protect against incorrect parameterization or the failure of the
transmission mechanisms. PROFIBUS DP uses monitoring mechanisms in the DP Master and in the DP
Slaves. They are implemented in the form of time monitors. The monitoring interval is specified in when the
DP system project is planned.
Protection mecha-
nisms
Description
At the DP Master
The DPM1 monitors the slave's transfer of user data with the Data_Control_Timer.
An individual monitoring timer is used for each assigned slave. The time monitor
triggers if a proper transfer of user data does not take place within the monitoring
interval. In this case the user is informed. If automatic error reaction is enabled
(Auto_Clear = True) then the DPM1 leaves the
Operate
state, switches the outputs
of the assigned slaves into a safe state, and then goes into the
Clear
operating state.
At the DP Slave
The slave uses communication monitoring in order to detect errors of the master or
in the transmission link. If data is not transferred with the assigned master within the
communication monitoring interval the slave switches the outputs into the safe state
itself. The slave inputs and outputs further require access protection in multi-master
systems, to ensure that direct access is only made from the authorized master. The
slaves will make an image of the inputs and outputs available to other masters, and
this can be read by any other master even if it does not have access authorization.
Ident number
Every DP slave and every DPM1 must have an individual identification number. This is required so that a DP
master can identify the types of the connected devices without any significant protocol overhead. The master
compares the identification numbers of the connected DP devices with the identification numbers in the
project planning data specified by DPM2. The transfer of user data only starts if the correct device types are
connected to the bus at the correct station addresses. This provides protection from project planning errors.
Manufacturer-specific identification numbers are issued by the PROFIBUS User Organization (PNO). The
PNO administers the identification numbers along with the basic device data (GSD).
6.1.2
PROFIBUS DP
In PROFIBUS DP systems a master (PLC, PC, etc.) usually communicates with many slaves (I/Os, drives,
etc.); only the master actively accesses the bus (by sending unsolicited telegrams), while a DP slave only
sends telegrams when requested by the master.
DP StartUp
Before the master and slave can cyclically exchange data, the parameter and configuration data is
transmitted from the master to the slaves during the DP StartUp phase. After the parameter and
configuration data has been sent, the master interrogates the slave's diagnostic data until the slave indicates
