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This is why the function CAN_ERRORHANDLER should be
used which registers all CAN error states and, if necessary,
resets the CAN controller. At the same time an error counter is
available to the application program. It could for example be
used to take further action depending on the count (e.g. error
LED).
But a detailed error analysis can only be performed by means of
an exact evaluation of the error bits.
6.4. The physical CAN link
The data transmission and error handling mechanisms
described in sections 6.2 and 6.3 are directly implemented in
the CAN controller. The physical link of the individual CAN
participants is described in layer 1 in ISO 11898.
Network structure
The standard ISO 11898 assumes a line-structured set-up of
the CAN network.
In addition, the line must be fitted with a terminating
resistor of 120
Ω
ΩΩ
Ω
at its two ends. In principle, ifm
electronic's devices fitted with a CAN interface have no
terminating resistors.
Ideally, no spur should lead to the bus participants (node 1 ...
node n) because depending on the total cable length and the
transmission time reflections occur in the bus. To avoid this
leading to system errors, the spurs to a bus participant (e.g. I/O
module) should not exceed a certain length. 2 m spurs are
considered to pose no problem. The sum of all spurs in the
whole system should not exceed 30 m. In special cases the
cable lengths of the line and the spurs must be accurately
calculated.
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