Manual 37364A GCP-30 Packages - Genset Control
CAN Bus Topology
NOTE
Please note that the CAN bus must be terminated with an impedance which corresponds to the wave
impedance of the cable (e.g. 120 Ω). The CAN bus is terminated between CAN-H and CAN-L.
The two CAN-H and CAN-L terminals in the unit are hard-wired internally and can be used to feed the
CAN bus through. However, if you want to avoid a break of the bus when a unit is unplugged, you may
connect the incoming and outgoing bus line in the same terminal.
GND
CAN-L
CAN-H
GND
GND
CAN-L
CAN-H
CAN-L
CAN-H
CAN-L
CAN-H
CAN bus
Termination
resistor
Note:
The termination has to be
performed with a resisitance,
which corresponds to the
impedance of the used cable
(e.g 120 Ohms)
CAN bus CAN bus
Termination
resistor
CAN-L
CAN-H
CAN-L
CAN-H
Figure 5-23: Interfaces - CAN bus topology
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 (stub-end feeders or branch lines are not recommended)
- CAN-L and CAN-H are interchanged
- Not all devices on the bus are using identical Baud rates
- Correct terminating resistor(s) is/are missing
- Incorrect baud rate (too high) for length of CAN bus
- 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 Table
5-24 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 kbits/s 1000 m
20 kbit/s 2500 m
Table 5-24: Maximum CAN bus length
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.
Page 40/46 © Woodward
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