ifm
System Manual
ecomat
mobile
PDM360NG (CR1080, CR1081, CR9042) Target V01
2011-07-28
CAN in the PDM360
Physical connection of CAN
163
9.2
Physical connection of CAN
Network structure ...................................................................................................................... 163
CAN bus level............................................................................................................................ 164
Bus cable length........................................................................................................................ 165
Wire cross-sections................................................................................................................... 166
1177
The mechanisms of the data transmission and error handling described in the chapters
Exchange of
CAN data
(
→
page
) and
CAN errors
(
→
) are directly implemented in the CAN controller.
ISO 11898 describes the physical connection of the individual CAN participants in layer 1.
9.2.1
Network structure
1178
The ISO 11898 standard assumes a line structure of the CAN network.
Figure: CAN network line structure
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.
Spurs
Ideally no spur should lead to the bus participants (node 1 ... node n) because reflections occur
depending on the total cable length and the time-related processes on the bus. To avoid system
errors, spurs to a bus participant (e.g. I/O module) should not exceed a certain length. 2 m spurs
(referred to 125 kbits/s) are considered to be uncritical. The sum of all spurs in the whole system
should not exceed 30 m. In special cases the cable lengths of the line and spurs must be calculated
exactly.
