Westermo RM-455U-D - Manual (Page 8)

Chapter One Introduction
Man_455U-D Rev 3.04 Page 9
Ordering Information
455U - Type – Radio Type – RF Power – Channel – Band – Frequency
Type D Data modem, full functionality
B Data modem, Bell 202 or V23 messaging
A External modem, 600 ohm audio input
C Data modem compatible with ELPRO 405U
Radio Type L 10 – 500mW H 0.5 – 5W
Power Actual power requested - for example, 100mW or 2W
Channel N 12.5 KHz W 20/25 KHz
Band 390 380 – 400 MHz 410 400 – 420 MHz
430 420 – 440 MHz 440 430 – 450 MHz
460 450 – 470 MHz 480 470 – 490 MHz
500 490 – 512 MHz
Frequency Actual frequency requested in MHz - for example, 471.0725
for different transmit and receive frequencies, enter Rxxxxx/Txxxxxx,
for example, R460.5000/T472.3000
1.1.1 Basic Operation
The operation of the 455U-D radio modem is relatively simple. As data is received at the
serial port, the data is transmitted on the radio channel. Up to 1020 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
number of bytes transmitted equals the maximum message length (user configurable - default
1020 bytes). If more than 1020 bytes is input, the 455U-D unit will transmit the first 1020
bytes, then the next 1020 bytes, and so on until all of the data has been transmitted.
Because the radio data rate could be less than the input serial data rate, an input memory
buffer of up to 8Kbytes is provided. The RS232 connection provides CTS control to prevent
the buffer overflowing. There are no data flow control signals for RS485.
1.1.2 Operating Modes
A radio channel cannot provide as secure a data channel as a wired connection. The 455U-D
uses a radio band with a low level of natural or industrial noise, however there is a chance of
interference from other users on the radio channel. We recommend that the flow of data over
the radio channel is controlled by using error detection and “handshaking” - that is, returning
an acknowledgment transmission if a data packet is received on the radio channel without
error. This function can be performed by either the host devices or the 455U-D modules.
The modules may be configured by the user to operate in one of two modes. In
Unacknowledged mode, it is assumed that the host devices control the flow of data - the
455U-D does not provide handshaking. In Acknowledged mode, the 455U-D units provide
handshaking to control the flow of data.
The RS485 port always operates in Unacknowledged mode.