Comtrol Modbus TCP User Guide - Manual (Page 14)

14 - Chapter 1. Introduction DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I
Definitions and Terms
1.5. Definitions and Terms
This section describes the Modbus/TCP definitions and terms included in the Modbus/TCP interface and
supported by the DeviceMaster UP.
1.5.1. Data Type Definitions
The following list defines the available data types.
1.5.2. Glossary
The following list defines terms associated with Modbus/TCP.
Data Type Definition
BYTE Bit String (8-bits)
DINT Signed Double Integer (32-bits)
DWORD Bit String (32-bits)
INT Signed Integer (16-bits)
STRING Character String (1-byte per character)
UDINT Unsigned Double Integer (32-bits)
USINT Unsigned Short Integer (8-bits)
WORD Unsigned Integer (16-bits)
Term Definition
Alias Device ID
The device ID that the original received ID is changed to when an Alias Device ID is
configured.
Device ID
The address of the slave device and the term is identical to Unit Identifier and Slave
Address.
Ethernet Device A device that communicates through an Ethernet TCP/IP connection.
Master Device
A device that transmits Modbus/TCP messages to slave devices and receives the
corresponding responses.
Modbus
An application layer messaging protocol that provides client/server communications
between devices connected on different types of buses.
Modbus Serial The Modbus protocol over a serial connection.
Modbus/ASCII
Modbus Serial in ASCII format. This form of Modbus communication requires two
characters for each byte.
Modbus/RTU Modbus Serial in binary format.
Modbus/TCP
The Modbus protocol over an Ethernet TCP/IP connection. Also known as Modbus over
Ethernet.
Raw Serial
Device A common serial device that communicates over serial ports through plain byte or ASCII
data messages.
Slave Address The address of the slave device. This term is identical to Unit Identifier and Device ID.
Slave Device A device that only responds to Modbus messages.
Socket Port The Ethernet socket port that is used to communicate to an Ethernet device.