Modbus Bus Couplers BK7300
Power LEDs
Bus Coupler
Input for
power contacts
Power contacts
Fieldbus connection
Address selector
Configuration interface
Address selector
Modbus Bus Couplers BK7350
Status display
power LEDs
Bus Coupler
Input for
power contacts
Power contacts
Fieldbus connection
Address selector
Configuration interface
Address selector
extended temperature range

BK7300, BK7350 | Modbus Bus Couplers

ModbusThe BK73x0 Bus Couplers connect the Modbus bus system to the modular, extendable electronic terminal blocks. One unit consists of one Bus Coupler, any number from 1 to 64 terminals and one end terminal. The “Compact” BK7350 Bus Coupler is a cost-optimised version with compact housing. With the K-bus extension, up to 255 Bus Terminals can be connected.

The Bus Couplers recognise the terminals to which they are connected, and perform the assignment of the inputs and outputs to the words of the process image automatically. The first input/output signal will be added to the first bit of a word (LSB), beginning from the left. The Bus Coupler adds further signals to the word. A clear separation is maintained between inputs and outputs. If the number of inputs or outputs is greater than 16 bits, the Bus Coupler automatically begins a new word.

Modbus has a line topology based on the RS485 interface. The Modbus protocol is published. The BK73x0 support the RTU and ASCII protocols. The baud rate is variable and can be set directly via the rotary selection switch on Bus Coupler, i.e. without configuration software.

The Modbus Bus Couplers support various Modbus functions that enable direct access to digital and analog signals. The BK7300 and BK7350 also support the diagnostic Modbus function that enables faults to be detected and counted. In addition, the Bus Couplers diagnose faulty or erroneous telegrams and respond to the controller with an error. BK7300 and BK7350 enable broadcast access, which means that several Bus Couplers can be addressed simultaneously with a single telegram.

System data Modbus | BK7300, BK7350
Number of I/O stations 99
Number of I/O points depending on controller
Data transfer medium screened, twisted copper cable 2 x 0.25 mm² (RS485)
Max. cable length 1,200 m
Data transfer rates 150 baud…38,400 baud
I/O communication types read/write access, optionally bit oriented or word oriented
Technical data BK7300 BK7350
Number of Bus Terminals 64 64 (255 with K-bus extension)
Max. number of bytes fieldbus 512 byte input and 512 byte output
Digital peripheral signals 512 inputs/outputs 1,020 inputs/outputs
Analog peripheral signals 256 inputs/outputs
Protocol RTU/ASCII (default: RTU)
Configuration possibility by rotary switch or KS2000
Bus interface D-sub 9-pin, RS485
Power supply 24 V DC (-15 %/+20 %)
Input current 70 mA + (total K-bus current)/4, 500 mA max. 320 mA max.
Starting current 2.5 x continuous current
Recommended fuse ≤ 10 A
Current supply K-bus 1750 mA 1000 mA
Power contacts 24 V DC max./10 A max.
Electrical isolation 500 V (power contact/supply voltage/fieldbus)
Weight approx. 170 g approx. 100 g
Operating/storage temperature 0…+55 °C/-25…+85 °C -25…+60 °C/-40…+85 °C
Relative humidity 95 %, no condensation
Vibration/shock resistance conforms to EN 60068-2-6/EN 60068-2-27
EMC immunity/emission conforms to EN 61000-6-2/EN 61000-6-4
Protect. class/installation pos. IP 20/variable
Approvals CE, UL, Ex, GL CE, UL, Ex
KS2000 configuration software for extended parameterisation
Cordsets cordsets and connectors
Ordering information Description
BK7300 Modbus Bus Coupler for up to 64 Bus Terminals
BK7350 Modbus “Compact” Bus Coupler for up to 64 Bus Terminals (255 with K-bus extension)
BC7300 Modbus Bus Terminal Controller
Modbus For further Modbus products please see the system overview