HMS Intesis DA70A0G1V5A5N040 Manual page 17

M-BUS to Modbus TCP Server Gateway
7. Modbus System
7.1. General Description
The Modbus protocol is an application-layer messaging protocol developed by Modicon in 1979. It is used to
establish client-server communication between intelligent devices over different types of buses or networks. The
Intesis gateway supports Modbus TCP.
Modbus is a request/reply protocol and offers services specified by function codes. Modbus function codes are
elements of Modbus request/reply PDUs (Protocol Data Units).
7.2. ModBus Interface
The Intesis gateway acts as a server device in its Modbus interface; the interface for this model is the Ethernet
port. To access the points and resources of the gateway from a Modbus client device, you must specify the
Modbus register addresses configured inside the gateway as those configured inside the gateway corresponding
to the signals of the field device protocol.
7.3. Functions Supported
Table 1. Modbus functions
# Function
01 Read Coils
02 Read Discrete Inputs
03 Read Holding Registers
04 Read Input Registers
05 Write Single Coil
06 Write Single Register
15 Write Multiple Coils
16 Write Multiple Registers
If poll records are used to read or write more than one register, the range of addresses requested must contain
valid addresses; if not, the Intesis gateway will return the corresponding Modbus error code.
1
All registers are of 2 bytes , even if they are associated with signals of bit type on the other protocol's side. Its
content is expressed in MSB .. LSB.
Modbus error codes are fully supported. They are sent whenever a non-valid Modbus action or address is
required.
7.4. Modbus TCP
Modbus TCP communication is characterized basically by the embedding of the Modbus RTU protocol into
TCP/IP frames, which allows faster communication and a longer distance between client and server devices in
comparison with RTU communication over a serial line. Another benefit is using common TCP/IP infrastructure in
buildings and transmitting over WAN or the internet. It also allows the coexistence of one or more clients and, of
course, one or more server devices in a given network, all interconnected through a TCP/IP-based network.
Use the configuration tool to configure the IP settings of the gateway (DHCP status, own IP, netmask, and default
gateway) and the TCP port.
1
Default value, it can be configured to be 4 bytes if required.
2
MSB: most significant bit; LSB: less significant bit
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Read/Write
R
R
R
R
W
W
W
W
2
Modbus System
USER MANUAL Version 1.0.2