Bms Protocol; Bms Master; Commissioning Of An Rs-485 Network With Bms Protocol; Address Setting And Termination - Bender ISOMETER iso1685DP-425 Manual

Device communication
The max number of bus nodes is restricted to 32 devices. If more devices are to be con-
nected, Bender recommends the use of a DI1 repeater.

9.1.2 BMS protocol

This protocol is an essential part of the Bender measuring device interface (BMS bus pro-
tocol). 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, waits for their response and then carries
out the corresponding commands.
A device receives the master function by assigning bus address 1 to it.

9.1.3 BMS master

A master can query all measured values, alarm and operating messages from a slave. If
bus address 1 is assigned to a device, this device automatically operates as master, i.e. all
addresses between 1 and 150 are cyclically scanned for alarm and operating messages
via the BMS bus. If the master detects incorrect answers from a slave, the fault message
"Fault RS-485" will be output via the BMS bus.
The following fault causes may exist:
• Addresses are assigned twice
• A second master exists on the BMS bus
• Interference signals occur on the bus lines
• A defective device is connected to the bus
• Terminating resistors are not activated or connected
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Device communication

9.1.4 Commissioning of an RS-485 network with BMS protocol

• Interconnect terminals A and B of all bus devices in one line.
• Switch the terminating resistors on at the start and the end of the RS-485 network. If
a device at the end of the bus is not terminated, connect a 120 Ω resistor to termi-
nals A and B.
• Switch the supply voltage on.
• Assign the master function and address 1 to a bus-capable device.
• Assign addresses (2...90) to all other bus devices in consecutive order.

9.1.5 Address setting and termination

Correct address setting and termination is essential for proper functioning of the
isoxx1685xx-xxx series insulation monitoring device.
Risk of bus errors!
Double assignment of addresses on the respective BMS busses can cause
serious malfunctions.
CAUTION
• Ensure correct address setting and termination of the device!

9.1.6 Setting the BMS address

The ISOMETER® cannot switch on a potential termination at the BMS bus.
Even though this is not expected to cause communication problems, the
ISOMETER® should be operated as BMS slave if possible (BMS address > 1).
If no other device with master capabilities is available on the bus, the ISO-
METER® can be set to master (BMS address 1).
Before the ISOMETER® takes over the backup master function after being
switched on, it waits to see if another master connects to the system.
Waiting period: BMS address minus 1 = waiting period in minutes.
Example: The iso1685DP has BMS address 3. It waits 3 minus 1 minutes (=
2 minutes) for a master to connect.
Set the BMS address ((1)2...90) in the device menu via the following path:
Device settings > Interface > BMS > BMS address.
isoxx1685Dx-x25_D00272_06_M_XXEN/04.2020