IFM Electronic CR0451 - CAN in the PDM360; General about CAN

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ifm System Manual ecomatmobile BasicDisplay (CR0451) V01
CAN in the PDM360 General about CAN
9 CAN in the PDM360
General about CAN......................................................................................................................70
Physical connection of CAN.........................................................................................................73
Exchange of CAN data.................................................................................................................77
CAN-FBs on layer 2 (RAW-CAN).................................................................................................82
CAN units acc. to SAE J1939 ................................................................................................... 113
CAN POUs to CANopen ........................................................................................................... 143
CAN errors and error handling .................................................................................................. 207
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9.1 General about CAN
Topology.......................................................................................................................................70
CAN interfaces .............................................................................................................................71
System configuration....................................................................................................................72
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The CAN bus (Controller Area Network) belongs to the fieldbuses.
It is an asynchronous serial bus system which was developed for the networking of control devices in
automotives by Bosch in 1983 and presented together with Intel in 1985 to reduce cable harnesses
(up to 2 km per vehicle) thus saving weight.
9.1.1 Topology
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The CAN network is set up in a line structure. A limited number of spurs is allowed. Moreover, a ring
type bus (infotainment area) and a star type bus (central locking) are possible. Compared to the line
type bus both variants have one disadvantage:
 In the ring type bus all control devices are connected in series so that the complete bus fails if one
control device fails.
 The star type bus is mostly controlled by a central processor as all information must flow through
this processor. Consequently no information can be transferred if the central processor fails. If an
individual control device fails, the bus continues to function.
The linear bus has the advantage that all control devices are in parallel of a central cable. Only if this
fails, the bus no longer functions.
NOTE
The line must be terminated at its two ends using a terminating resistor of 120  to prevent corruption
of the signal quality.
The devices of ifm electronic equipped with a CAN interface have no
terminating resistors.
The disadvantage of spurs and star-type bus is that the wave resistance is difficult to determine. In the
worst case the bus no longer functions.
For a high-speed bus (> 125 kbits/s) 2 terminating resistors of 120  (between CAN_HIGH and
CAN_LOW) must additionally be used at the cable ends.