BECKHOFF BC3100 - Manual (Page 23)

PROFIBUS-DP basics
BC3100 23
timeout monitors. The monitoring interval is specified when the DP system
is planned.
On the DP master
The DPM1 uses the Data_Control_Timer to monitor the transfer of user
data to and from the DP slaves. A separate monitoring timer is used for
each of the subordinate DP slaves. If a monitoring interval elapses without
any data being transferred, the monitor will report a timeout. The user will
be informed if this occurs. If automatic error response has been specified
(Auto_Clear = True), the DPM1 will leave Operate mode, switch the
outputs of its DP slaves to a secure state and go into Clear mode.
On the DP slave
Each DP slave maintains a response monitor to enable it to recognize
errors in the DP master or the transfer route. If a response monitoring
interval elapses without any data being exchanged with the superordinate
DP master, the DP slave will independently switch its outputs to the secure
state. In the case of a multi-master system additional security is necessary
to restrict access to the inputs and outputs of the DP slaves and to ensure
that direct accesses are made only by the authorized master. The DP
slaves therefore provide the other DP masters with a mapping of their
inputs and outputs which can be read by any DP master, even without
authority.
Identity number Each DP slave and each DPM1 must have an individual identity number so
that a DP master can recognize the types of the attached devices without
entailing a significant protocol overhead. The master compares the identity
numbers of the attached DP devices with the identity numbers in the
planning data specified by the DPM2. No user data will be transferred
unless the correct device types have been attached to the bus with the
correct station addresses. This ensures that the system is protected from
planning errors.
Beckhoff PROFIBUS couplers, like all DP slaves and DPM1s, possess an
identity number allocated by the PNO. The PNO administers these identity
numbers together with the device master data and identity numbers are
also given in the type files.