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4.2 J1939 Network
J1939 is a higher-layer protocol based on Controller Area Network
(CAN). It provides serial data communications between microprocessor
systems (also called Electronic Control Units - ECU) in any kind of heavy
duty vehicles. The messages exchanged between these units can be data
such as vehicle road speed, torque control message from the transmission
to the engine, oil temperature, and many more.
4.2.1 Communication Methods
The GW-7228 provides two communication methods of SAE J1939,
each serving a specific purpose.
Destination Specific Communications
Destination specific communications use PDU1, but also the global
destination address 255. There are cases where this method will require
the utilization of destination specific Parameter Group Numbers, for
instance, in the case of more than one engine. A torque message, for
example, must be sent only to the desired engine and not to both.
Broadcast Communications
Broadcast communications use PDU2 and, as the name implies, they
can include: Sending a message from a single or multiple sources to a
single destination; sending a message from a single or multiple sources to
multiple destinations.
4.2.2 Parameter Groups
Parameters groups are, for instance, engine temperature which
includes coolant temperature, fuel temperature, oil temperature, etc. The
Parameter Groups (PG) architecture and Parameter Group Numbers
(PGN) are described in SAE J1939/21 and defined in SAE J1939/71.
GW-7228 J1939/Modbus RTU Slave Gateway User's Manual (Ver 1.3, Apr/2011) ------------- 32
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