ABB FENA-01, Protocol Manual

Page: 37 / 52

Communication
37
Communication
Overview
This chapter describes the Modbus/TCP communication protocol
for the FENA-01. For detailed information on Modbus/TCP
communication, refer to
• Modbus Application Protocol Specification v1.1a
• Modbus Messaging on TCP/IP Implementation Guide v1.0a
Register Addressing
The address field of Modbus Requests for accessing Holding
Registers is 16 bits. This allows the Modbus protocol to support
addressing of 65536 Holding Registers.
Historically, Modbus client devices used 5-digit decimal addresses
from 40001 to 49999 to represent Holding Register addresses. 5-
digit decimal addressing limited to 9999 the number of holding
registers that could be addressed.
Modern Modbus client devices typically provide a means to
access the full range of 65536 Modbus Holding Registers. One of
these methods is to use 6-digit decimal addresses from 400001 to
465536. This manual uses 6-digit decimal addressing to represent
Modbus Holding Register addresses.
Modbus client devices that are limited to 5-digit decimal
addressing may still access registers 400001 to 409999 by using
5-digit decimal addresses 40001 to 49999. Registers 410000-
465536 are inaccessible to these clients.