Modbus/Tcp Interface; Introduction; Modbus/Tcp Protocol; Parameter Addressing - Honeywell UDA2182 User Manual

Modbus/TCP Interface

5.1 Introduction

UDA2182 supports the Modbus/TCP (also called Modbus TCP/IP or Modbus Ethernet) protocol for
communications with third party HMI and SCADA software via a direct Ethernet TCP/IP connection.
The UDA's optional Ethernet 10/100Base-T Host port is used for the Modbus/TCP connection. Ethernet
TCP allows multiple concurrent connections to hosts for data interchange. The UDA supports 5 concurrent
host connections using Modbus/TCP protocol messaging via this port. The number of client hosts that can
access the UDA depends upon the ability of the applications to share these connections.

5.2 Modbus/TCP Protocol

Modbus/TCP protocol, developed by Groupe Schneider's Modicon Division, is a popular, open standard
for data interchange over Ethernet TCP/IP networks using a Modbus RTU command structure.
It is simply an encapsulation of Modicon's Modbus RTU protocol within a TCP/IP frame as shown below,
which includes header information and the Modbus frame.
The Open Modbus/TCP Specification is followed with respect to the physical, data link, and network layers. The
message structure within the Modbus frame uses standard Modbus RTU function codes.
The Address part of the Modbus frame is not used (set to 00) since there is no sub-addressing intended or required.
The UDA IP address is the identifying address, set independently at the UDA.
The error checking is supported by TCP/IP network protocols and not part of the Modbus frame.
The Transaction Identifiers and Protocol Identifiers in the header are normally all 0's (4 bytes total) while the
Length field identifies the number of bytes in the Modbus frame.
The standard IEEE 32-bit floating point, 32-bit and 16-bit integer formats are used. Both big and little endian
floating point word order are supported using a Modbus Word Swap configuration parameter.

5.3 Parameter Addressing

Shown in Sections 10 and 11 are maps listing the parameter addresses.
Examples for read or write access to parameters supported by the various function codes are provided in Section 8.
12
5. Modbus/TCP Interface

Figure 5-1 Modbus RTU Protocol within a TCP/IP Frame

UDA2182 Communications User Guide January 09