Modbus Interface - HMS Anybus Modbus to KNX Gateway User Manual

Product Description
3.4

Modbus Interface

Modbus TCP basically embeds the Modbus RTU protocol in TCP/IP frames. TCP/IP allows faster
communication and a longer distance between the master and slave devices than RTU
communication over serial line. Modbus TCP allows communication over an existing TCP/IP
infrastructure such as a LAN, WAN or the Internet. It also allows multiple Modbus masters to
exist in the same network.
The Modbus to KNX Gateway will act as a master in a Modbus TCP network or as a Modbus RTU
Master, or both. All other Modbus devices connected to the same network must be slave/server
devices.
Each Modbus TCP slave device has an IP address and a predefined register address map. The
address map defines the address, type and characteristics of each internal point (register) of the
device and makes this data accessible through the Modbus TCP protocol.
Each defined point can be configured with a slave address from 0 to 255. This allows for great
flexibility, for example to integrate Modbus RTU slave devices connected in a serial line with an
RTU/TCP converter enabling access to their data points through TCP/IP. The converter,
communicating in TCP, will then identify the destination of the point (slave address in the RTU
network) by the contents of the slave address field.
The Modbus TCP protocol defines different types of function codes to read/write different type
of registers in Modbus devices, and also different data encoding formats. Implementation can
vary between different slave device types and manufacturers. The data encoding and byte order
for 16-bit registers can be configured in the gateway.
The communication parameters (IP address, netmask, default router address and TCP port) of
the Modbus TCP interface are also fully configurable.
See also Modbus Points Definition, p.
Modbus to KNX Gateway User Manual
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SCM-1202-050 1.2 en-US