User's Manual

Chapter One Introduction
Man_455U Rev 1.0 Page 7
Chapter One INTRODUCTION
1.1 General
The 455U radio modem module has been designed to provide flexible and reliable radio
modem functions, at an economical price. Radio modems transmit serial data over a long
distance via radio. The serial data is not changed - the output data is the same as the input
data. Although the 455U is intended to be simple in its application, it also provides many
sophisticated features. This manual should be read carefully to ensure that the modules are
configured and installed to give reliable performance.
Each 455U module will connect to a host device by RS232 or RS485 serial connection.
Examples of host devices are PLC’s, data loggers, intelligent transducers and computers. The
455U unit can receive data from the host device and transmit this data by radio to another (or
several) 455U module. The other module will recreate the serial data and output it as either a
RS232 or RS485 serial signal. The 455U unit provides two-way communications - each
module can accept serial data and also output serial data.
The 455U module includes power supply, microprocessor controller, serial input/output
circuits and a fixed frequency radio transceiver (range from 360Mhz to 520Mhz) - no external
electronics are required. The units are configured from a PC using a Microsoft Windows
“free-ware” configuration package, or from a PC terminal using Hayes commands.
RS232 is an electrical standard format for a full
duplex point-to-point serial connection. RS485
is an electrical standard format for a half-duplex
multidrop serial connection. Up to 32 devices
can communicate on a common RS485 serial
bus. Each 455U can simultaneously connect to
signals from both RS232 and RS485. In
addition, RS232 data from one host device can be
transmitted to a remote 455U unit and output as RS485 data to another host device.
The 455U has been designed to be flexible enough to cover a wide range of applications. The
user is able to configure many different parameters such that the 455U unit will connect
reliably to different types of host devices. Before the radio modem can be used, these
parameters must be configured. Some of these parameters are :-
• Character type - the 455U will accept a variety of 7 or 8 data bit characters
• RS232 Serial Data Rate - between 1200 and 115,200 bits/sec
• RS485 Serial Data Rate - between 1200 and 187,500 bits/sec
• Radio Data Rate - 1200 to 19,200 bits/sec
• Operating mode - unacknowledged mode, Acknowledged mode, Host Protocol Specific
modes (DF1, Modbus, Profibus, DNP3), Remote Configuration and Diagnostics mode.
The operation of the 455U radio modem is relatively simple. As data is received at the serial
port, the data is transmitted on the radio channel. Up to 1024 bytes of data can be
transmitted in one transmission. The radio transmission commences when the first data byte
is received, and ends when there are no more data bytes in the input buffer, or when the
HOST
455U
RS232
HOST
455U
RS485