ifm
System Manual
ecomat
mobile
SmartController (CR2500) V05
CAN in the ecomatmobile controller
General about CAN
47
8
CAN in the ecomatmobile controller
General about CAN ...................................................................................................................47
Exchange of CAN data ..............................................................................................................49
Physical connection of CAN ......................................................................................................51
Software for CAN and CANopen ...............................................................................................55
CAN errors and error handling ..................................................................................................55
Description of the CAN functions...............................................................................................58
ifm CANopen library...................................................................................................................83
Summary CAN / CANopen ..................................................................................................... 144
Use of the CAN interfaces to SAE J1939 ............................................................................... 145
8.1
General about CAN
The CAN bus (
C
ontroller
A
rea
N
etwork) 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.
8.1.1
Topology
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.
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
Ω
(between CAN_HIGH and
CAN_LOW) must additionally be used at the cable ends.
