Furuno CAN bus Network Design Guide
13
1.10 CAN bus Network Limitations
When building a CAN bus network, keep in mind following limitations.
1.10.1 Single MFD in CAN bus network
Single MFD or DRS unit, one of MFD8, MFD12, MFDBB, and DRS is connected to a Furuno
CAN bus network. Do NOT connect two or more MFD and/or DRS to the Furuno CAN bus
network. The DRS and MFD units are connected each other via Ethernet.
Fig.35 Single MFD or DRS in Furuno CAN bus network
1.10.2 Backbone Cable Length
Load Equivalency Number (LEN)
Like NMEA2000, the power rating of the Furuno CAN bus device is specified as a Load
Equivalency Number, or LEN and used in planning network installations. One network load is
defined as 50 mA or any portion thereof (e.g., a device taking 51 mA from the network power
bus is a Two LEN device). A LEN of 4 means that the device consumes up to 4 x 50 mA = 200
mA.
Table 6 shows the LEN of Furuno CAN bus devices.
Table 6 LEN of Furuno CAN bus devices
Model
MFD BB MFD 8/12 SC-30
GP-330B
WS-200 FI-50 series*
LEN
1
1
10
3
13
2
*: FI-501/502/503/504/505/506
Use Tables 7 and 8 to find the maximum length of the backbone cable. First calculate the total
LEN of the devices in the network. In the example of Fig.36, the total LEN is 1+ 1 + 2 +2 = 6.
Then, find the maximum cable length for the LEN of 6 in Table 7 or 8: 150 meters for heavy
cable and 50 meters for light cable when the network is powered from 15 Vdc power supply.
When the network is connected to 12 Vdc power supply, the maximum cable length is about
half the value in Tables 7 and 8.
Fig.36
CAN bus
Device
LEN = 1
CAN bus
Device
LEN = 1
CAN bus
Device
LEN = 2
CAN bus
Device
LEN = 2
Power supply
Power supply
MFD
(DRS)
Device
MFD
(DRS)
