Hirschmann GREYHOUND GRS1020, Reference Manual

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Industry Protocols
15.2 Modbus TCP
238
UM Config GRS
Release 8.0 09/2019
15.2 Modbus TCP
Modbus TCP is an application layer messaging protocol providing client/server communication
between the client and devices connected in Ethernet TCP/IP networks.
The Modbus TCP function lets you install the device in networks already using Modbus TCP and
retrieve information saved in the registers in the device.
15.2.1 Client/Server Modbus TCP/IP Mode
The device supports the client/server model of Modbus TCP/IP. This device operates as a server
in this constellation and responds to requests from a client for information saved in the registers.
The client / server model uses four types of messages to exchange data between the client and
server:
Figure 54: Client/Server Modbus TCP/IP Mode

Modbus TCP/IP Request, the client creates a request for information and sends it to the server.

Modbus TCP/IP Indication, the server receives a request as an indication that a client requires
information.

Modbus TCP/IP Response, when the required information is available, the server sends a reply
containing the requested information. When the requested information is unavailable, the server
sends an Exception Response to notify the client of the error detected during the processing.
The Exception Response contains an exception code indicating the reason for the detected
error.

Modbus TCP/IP Confirmation, the client receives a response from the server, containing the
requested information.
15.2.2 Supported Functions and Memory Mapping
The device supports functions with the public codes 0x03 ( Read Holding Registers ) and 0x05
( Write Single Coil ). The codes allow the user to read information saved in the registers such as
the system information, including the system name, system location, software version, IP address,
MAC address. The codes also allow the user to read the port information and port statistics. The
0x05 code lets the user reset the port counters individually or globally.
The following list contains definitions for the values entered in the Format column:

Bitmap: a group of 32-bits, encoded into the Big-endian byte order and saved in 2 registers. Big-
endian systems save the most significant byte of a word in the smallest address and save the
least significant byte in the largest address.

F1: 16-bit unsigned integer

F2: Enumeration - power supply alarm
– 0 = power supply good
– 1 = power supply failure detected

F3: Enumeration - OFF/ON
– 0 = Off
– 1 = On
Modbus
Client Modbus
Server
Request Indication
Confirmation Response