Applications - CAN System Engineering - page 271

Fig. 5.14 Smoke detection system using an open standard controller area network (CAN) bus-to-
interface detector
Analysis of the communication needs to result in the following protocol require-
ments:
• Every individual smoke detector on the network must be uniquely identifiable,
• Messages generated by a smoke detector must contain information about its
identity and
• The detector must support a master-slave communication model.
CAN Identifier The 29-bit extended identifier is utilized and partitioned into the
subfields as shown in Fig. 5.15 .
Message Type The purpose of the Message Type is to categorize messages accord-
ing to their overall relative priority and indicate whether the Module ID contains a
transmitter or receiver address. Two classes of Message Type, Process Data Object
(PDO) and Service Data Object (SDO) are instantiated either as Transmit or as
Receive objects, T_PDO and R_PDO as well as T_SDO and R_SDO, respectively.
A Transmit Data Object (T_xDO) denotes that Module ID contains the network
address of the transmitter, whereas a Receive Data Object (R_xDO) contains the
network address of the intended receiver in the Module ID field.