BECKHOFF BC3150 - Manual (Page 86)

Safety Instructions
84 Fieldbus Components
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 distributed 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
mechanisms
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 mode.
At the DP
Slave The slave uses communication monitoring in order to detect errors of the master or in the
transmission segment. 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).