
Manual 37135C
IKD 1 - Digital I/O Expansion Board
© Woodward
Page 11/41
Possible CAN Bus Problems
If no data is transmitted on the CAN bus, check the following for common CAN bus communication problems:
•
T structure bus is utilized
•
CAN-L and CAN-H are interchanged
•
Not all devices on the bus are using identical Baud rates
•
Terminating resistor are missing
•
Baud rate to high for wiring length
•
The CAN bus cable is co-routed with power cables
Woodward recommends the use of twisted-pair cables for the CAN bus (i.e.: Lappkabel Unitronic LIYCY (TP)
2×2×0.25, UNITRONIC-Bus LD 2×2×0.22).
Maximum CAN bus Length
The maximum length of the communication bus wiring is dependent on the configured Baud rate. Refer to the fol-
lowing table for the maximum bus length (Source: CANopen; Holger Zeltwanger (Hrsg.); 2001 VDE VERLAG
GMBH, Berlin und Offenbach; ISBN 3-8007-2448-0).
Baud rate
Max. length
1000 kbit/s 25 m
800 kbit/s
50 m
500 kbit/s
100 m
125 kbit/s
250 m
50 kbit/s
1000 m
20 kbit/s
2500 m
The maximum specified length for the communication bus wiring might not be achieved if poor quality wire is
utilized, there is high contact resistance, or other conditions exist. Reducing the baud rate may overcome these is-
sues.
Shielding
Interface
CAN bus
CAN-L
CAN-H
GND
Shield
1 M
Ohm
0.01
µ
F
400 Vac
Figure 3-7: Interface - shielding of CAN bus