BMS and CAN bus
32
isoPV1685-1685PFR_D00007_02_M_XXEN/10.2016
6.1.2
Topology RS-485 network
The optimum topology for an RS-485 network is a daisy-chain connection. In this connection,
device 1 is connected to device 2, device 2 to device 3, device 3 to device n etc. The RS-485 network
represents a continuous path without branches.
Correct arrangement
Three examples for correct arrangement:
Wrong arrangement
Three examples for wrong arrangement:
Wiring
The suitable type of wiring for the RS-485 network is:
shielded cable, core diameter
≥
0.8 mm
(e.g. J-Y(St)Y2x0.8), shield connected to earth (PE) on one end.
Connection to the terminals A and B.
The number of bus nodes is restricted to 32 devices. When more devices are to be connected,
Bender recommends to use a DI1 repeater.
6.1.3
BMS protocol
This protocol is an essential part of the Bender measuring device interface (BMS bus protocol).
Data transmission generally makes use of ASCII characters.
Interface data are:
•
Baud rate:9600 baud
•
Transmission:1 start bit, 7 data bits, 1 parity bit, 1 stop bit (1, 7, E, 1)
•
Parity:even
•
Checksum:Sum of all transmitted bytes = 0 (without CR and LF)
The BMS bus protocol works according to the Master-Slave principle. Only one master may exist in
each network. All bus devices are identified by a unique BMS address. The master cyclically scans all
other slaves on the bus, listens to their signals and then carries out the corresponding commands.
A device receives the MASTER function by assigning
Bus address 1
to it.
DI1
1
32
33
64
