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isoPV1685-1685PFR_D00007_02_M_XXEN/10.2016
6. BMS and CAN bus
6.1 BMS bus
6.1.1
RS-485 interface with BMS protocol
The RS-485 interface, galvanically isolated from the device electronics, serves as a physical transmis-
sion medium for the BMS protocol. When an isoPV1685…or other bus devices are interconnected
via the BMS bus in a network, the BMS bus must be terminated at both ends with a 120 Ω resistor.
For this purpose, the device is equipped with the terminating switch SS8100.
An RS-485 network that is not terminated is likely to get instable and may result in malfunctions.
Only the first and the last device in one line may be terminated. Stub feeders in the network are not
to be terminated. The length of the stub feeders is restricted to 1 meter.
Fig. 6.1: Wiring and termination of the BMS bus with SS8100
on the pcb or enclosure
maximum length of the RS-485 network: 1200 m
1. device
… device
last device
stub feeder
max. 1 m
A1 A2
E KE
21 22 24
31 32 34
k l kT IT
A B S
RS-485
Term.
off on
CAN 1
CAN 2
I2+ I2- I1+ I1-
K3
K2
11 12 14
K1
I2+ I2- I1+ I1-
A B S
k I kT IT
31 32 34
21 22 24
11 12 14
E KE
A1 A2
A B S
RS-485
Term.
off on
CAN 2
A B S
A B S
CAN 2
A B S
