Wachendorff WDGA 58V handleiding
Handleiding
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Technical Manual
WDGA with CANopen Interface
5 - General information about CAN
© Wachendorff Automation GmbH & Co. KG
11
5 General information about CAN
5.1 CAN physical and transport layer
CAN is a field bus. It operates with the CSMA/CA (Carrier Sense Multiple Access /
Collision Avoidance) method. It means that collisions during bus access are avoided
by a so called bitwise arbitration. The bits are coded NRZ-L (Non Return to Zero - Low).
A cyclic redundancy check (CRC) and other safety mechanisms provide a secure
transmission. For synchronisation a mechanism called "bit stuffing" is used. CAN is a
multi-master system, i.e. several equal bus nodes can be connected without a bus
master supervising the communication. In principle a CAN bus can be realized with
copper wire or in fibre optic cable.
The common CAN implementation with copper wire operates with differential signals,
transmitted via two wires: CAN
HIGH
, CAN
LOW
. Therefore CAN has a good common
mode rejection ratio.
Data is transmitted with bits that can either be dominant or recessive. The dominant
(0) always overwrites the recessive (1).
The topology of a CAN network is a line, which can be extended by stubs. The
maximum length of a stub is limited to 0,5m.
The network always has to be terminated on both ends with 120Ohms each (between
CAN
HIGH
und CAN
LOW
). Other locations or values are not allowed.
The arbitration mentioned before is used to control the bus access of the nodes by
prioritization of the CAN-Identifier of the different messages. Every node monitors the
bus. If more than on node wants access on the bus, the node with the highest priority
of the messages ID succeeds and the other nodes retreat until there is "silence" on
the bus (see Figure 5.1). Technically the first dominate bit of the ID send overwrites
the corresponding recessive bit of the other IDs. In case that more than one node
uses the same CAN-ID an error occurs only at a collision within the rest of the frame.
On principle a CAN-ID should only be used by a single node!
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Productinformatie
| Merk | Wachendorff |
| Model | WDGA 58V |
| Categorie | Niet gecategoriseerd |
| Taal | Nederlands |
| Grootte | 11685 MB |
