Civil Engineering Reference
In-Depth Information
Fig. 5.16
Normal configuration check request/reply process
Fig. 5.17
Failure of expected smoke detector to reply
with the broadcast Module ID to all smoke detectors. These in turn reply with T_
PDOs containing their individual Module Address, enabling the network master to
make a comparison of the received replies with the expected replies and, thereby,
detect the following failure cases (Figs.
5.16
,
5.17
and
5.18
):
• The network master is incorrectly configured for the intended installation,
• An expected smoke detector has not replied (missing smoke detector on net-
work) and
• An unexpected smoke detector has replied (excessive smoke detector on network).
Thus, comparison of the configuration present on the network with the expected
configuration is a prerequisite for determined network behaviour.
5.3.4.6
Normal Polling Operation
The CAN bus is operated in the master-slave mode (Fig.
5.19
). The network master
cyclically acquires the status of each smoke detector by an explicitly addressed re-
quest frame. Not to be confused with CAN remote-request frames, the request mes-
sage is a regular data frame of type R_PDO containing the individual Module ID of
the subject smoke detector and is replied to by a T_PDO data frame containing the
Module ID of the replying transmitter.
