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Input/ Output 5-17MN1942

5.5 CAN interface
TheCAN bus is a s erial based network originally developed for automotiveapplications, butnow
used for a wide range of industrial applications. Itoffers low-cost serial c ommunications with
very high reliability in an industrial environment; the probability of an undet ected error is
4.7x10-11. It is optimized for the transmission of small data packets and therefore offers fast
updateof I/O dev ices (peripheral devices) connected to the bus .
The CAN protocol only defines the physical attributes of the network, i.e. the electrical,
mechanical, functional and procedural parameters of the physical connection between devices.
The higher level network functionality on MicroFlex e100 is defined by the CANopen protocol,
oneof the most us ed standards for machine control.

5.5.1 CAN conn ector

Location CAN
Matingconnec tor: 9-pin female D-type
Pin Name Description
1 - (NC)
2CAN- CAN channel negative
3CANGND Ground/earth refer ence for CAN signals
4 - (NC)
5Shield Shieldc onnection
6CANGND Ground/earth refer ence for CAN signals
7CAN+ CANc hannel positive
8 - (NC)
9CANV+ CANpow er V+ (12-24V)

5.5.2 CAN wiring

Av ery low error bit rate over CAN can only be achiev ed with a suitable wiring scheme, so the
followingpoints should be observed:
HThe two-wire data bus line may be routed parallel, twisted and/or s hielded, depending on
EMC requirements. Baldor recommend a twisted pair c able with the shield/screen
connectedto the connector backshell,in order to reduce RF emiss ions and provide immunity
toconduc ted interference.
HThebus must be ter minated at both ends only (not at intermediate points) with resis tors of a
nominalvalue of 120Ω. This is to reduce reflections of the electrical signals on the bus, which
helpsa node to interpret the bus voltagelev els correctly. If the MicroFlex e100 is at the end
of the network then ensure that a 120Ωresistor is fitted (normallyinside the D-type
connector).
HAllcables and connectors should have a nominal impedance of 120Ω. Cables should have
alength related res istance of 70mΩ/m and a nominal line delay of 5ns/m.
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