User manual

Chapter One Introduction
Page 7 © January 2011
Chapter One INTRODUCTION
1.1 General
The 905U-D 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 905U-D 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 905U-D 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
905U-D unit can receive data from the host device and transmit this data by radio to another (or
several) 905U-D module. The other module will recreate the serial data and output it as either a
RS232 or RS485 serial signal. The 905U-D unit provides two-way communications - each
module can accept serial data and also output serial data.
The 905U-D module includes power supply, microprocessor controller, serial input/output
circuits and a 900MHz frequency-hopping spread-spectrum radio transceiver - no external
electronics are required. The 905U-D radio frequency has been selected to meet the requirements
of unlicensed operation for remote monitoring and control of equipment. That is, a radio licence
is not required for the 905U-D modules in many countries. See Chapter Five Specifications for
details. The units are configured from a PC using a “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 905U-D unit can only connect to one
serial signal - either RS232 or RS485.
However different modules in the same system
can connect to different types of serial signals. For example, RS232 data from one host device
can be transmitted to a remote 905U-D unit and output as RS485 data to another host device.
The 905U-D 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 905U-D 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 905U-D will accept a variety of 7 or 8 data bit characters
• Serial Data Rate - between 1200 and 115200 bits/sec
• Radio Data Rate - 19200, 57600 or 115200 bits/sec
• Operating mode - transparent mode or controlled mode .
HOST
905U-D
RS232
HOST
905U-D
RS485