MTL WMO-800S User manual
WMO-800S
Radio Modem
User Guide
INM WMO800S
WMO-800S Radio Modem Module
Page 2 June 2010
User Manual
INM WMO800S_v1.8.doc Page 3
Thank you for your selection of the WMO-800S radio modem.
We trust it will give you many years of valuable service.
ATTENTION!
Incorrect termination of supply wires may
cause internal damage and will void warranty.
To ensure your WMO-800S enjoys a long life,
double check ALL your connections
with the user’s manual
before turning on the power.
WMO-800S Radio Modem Module
Page 4 June 2010
How to Use This Manual
To receive the maximum benefit from your WMO-800S product, please read the
Introduction, Installation and Operation chapters of this manual thoroughly
before putting the WMO-800S to work.
Chapter Four Configuration details the configurations available and explains
the diverse operation of the product in detail.
Chapter Five Specifications details the features of the product and lists the
standards to which the product is approved.
Chapter Six Troubleshooting will help if your system has problems.
The WMO-800S Installation Guide supplied is an installation drawing
appropriate for most applications.
WARNING
1. In some countries, a radio licence is not required for the WMO-800S
telemetry modules provided the module is installed using the antenna and
equipment configuration prescribed.
2. Where a radio licence is not required, operation is authorised by the
relevant Authority in your country on a non-protection basis. Although
all care is taken in the design of these units, there is no responsibility
taken for sources of external interference. Some delay in the operation
of the module may occur during periods of interference. Systems should
be designed to be tolerant of these delays.
3. To avoid the risk of electrocution, the antenna, antenna cable, and all
terminals of the WMO-800S module should be electrically protected. To
provide maximum surge and lightning protection, the module should be
connected to a suitable earth and the antenna, antenna cable, and the
module should be installed as recommended in the Installation Guide.
4. To avoid accidents during maintenance or adjustment of remotely
controlled equipment, all equipment should be first disconnected from the
WMO-800S module during these adjustments. Equipment should carry
clear markings to indicate remote or automatic operation. eg. "This
equipment is remotely controlled and may start without warning. Isolate
at the switchboard before attempting adjustments."
5. The WMO-800S module is not suitable for use in explosive environments
without additional protection.
User Manual
INM WMO800S_v1.8.doc Page 5
CONTENTS
WARNING ...............................................................................................................................4
CHAPTER ONEINTRODUCTION...............................................................................7
1.1GENERAL ........................................................................................................................7
1.2TRANSPARENT MODE .....................................................................................................8
1.3CONTROLLED MODE.......................................................................................................9
1.4REPEATER UNITS ..........................................................................................................10
CHAPTER TWOINSTALLATION..............................................................................11
2.1GENERAL ......................................................................................................................11
2.2ANTENNA INSTALLATION..............................................................................................11
2.2.13dB/6dB Collinear antenna......................................................................................12
2.2.2Yagi antennas...........................................................................................................13
2.3POWER SUPPLY.............................................................................................................14
2.4SERIAL CONNECTIONS ..................................................................................................14
2.4.1 RS232 Serial Port........................................................................................................14
2.4.2 RS485 Serial Port........................................................................................................15
CHAPTER THREEOPERATION...................................................................................16
3.1POWER-UP AND NORMAL OPERATION...........................................................................17
3.2SERIAL AND RADIO DATA.............................................................................................17
3.2.1Character Type.........................................................................................................18
3.2.2Serial Data Rate .......................................................................................................18
3.2.3Radio Data Rate.......................................................................................................18
3.3ADDRESSING.................................................................................................................19
3.4TRANSPARENT MODE ...................................................................................................19
3.5TRANSPARENT MODE REPEATERS ................................................................................20
3.6CONTROLLED MODE.....................................................................................................21
3.6.1 Auto-Connect Controlled Mode .................................................................................24
3.6.2 Low Power Auto-Connect Mode...............................................................................24
3.6.3 Single-Connect Controlled Mode..............................................................................24
3.6.4Fast Operation Controlled Mode Not used...........................................................25
3.6.5 CTS/RTS Flow Control .............................................................................................25
3.6.6 Intermediate Repeaters................................................................................................25
3.7WHAT OPERATING MODE TO USE ?..............................................................................26
3.7.1Transparent or Controlled Mode?............................................................................26
3.7.2Error Check ?...........................................................................................................26
3.8SERIAL /RADIO RATES .................................................................................................26
3.9OPERATING PROBLEMS.................................................................................................27
WMO-800S Radio Modem Module
Page 6 June 2010
CHAPTER FOURCONFIGURATION...........................................................................28
4.1BEFORE CONFIGURING..................................................................................................28
4.2ADDRESSING.................................................................................................................28
4.3DEFAULT CONFIGURATION ...........................................................................................29
4.4CONFIGURATION PROGRAM ..........................................................................................29
4.4.1Transparent Mode....................................................................................................30
4.4.2Controlled Mode......................................................................................................31
4.4.3Other Parameters......................................................................................................33
4.5HAYES COMMANDS ......................................................................................................36
4.6CONFIGURATION EXAMPLES.........................................................................................41
4.7SWITCH CONFIGURATION..............................................................................................43
CHAPTER FIVESPECIFICATIONS..............................................................................45
CHAPTER SIXTROUBLESHOOTING .........................................................................47
6.1DIAGNOSTICS CHART....................................................................................................47
6.2TEST FUNCTIONS ..........................................................................................................47
6.2.1Radio Testing - AT&Tx...........................................................................................47
6.2.2Bit Error Rate Test (BER) .......................................................................................49
6.2.3On-line diagnostics..................................................................................................49
APPENDIX A HAYES COMMANDS.............................................................................50
User Manual
INM WMO800S_v1.8.doc Page 7
Chapter One INTRODUCTION
1.1 General
The WMO-800S 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 WMO-800S 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 WMO-800S 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 WMO-800S unit can receive data from the host device and transmit this data
by radio to another (or several) WMO-800S module. The other module will recreate the
serial data and output it as either a RS232 or RS485 serial signal. The WMO-800S unit
provides two-way communications - each module can accept serial data and also output serial
data.
The WMO-800S module includes a power supply, microprocessor controller, serial
input/output circuits and an 869MHz fixed frequency radio transceiver - no further external
electronics are required. The WMO-800S 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 WMO-800S modules in many countries. See Chapter
Five Specifications for details. The units are configured from a PC using a “freeware”
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
multi-drop serial connection. Up to 32 devices
can communicate on a common RS485 serial
bus. Each WMO-800S 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 WMO-800S unit and output as RS485 data to another
host device.
The WMO-800S 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 WMO-
800S 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 WMO-800S will accept a variety of 7 or 8 data bit characters
Serial Data Rate - between 1200 and 115200 bits/sec
Radio Data Rate - 19200, 38400 or 76800 bits/sec
Operating mode - transparent mode or controlled mode.
HOST
800S
RS232
HOST
800S
RS485
WMO-800S Radio Modem Module
Page 8 June 2010
The operation of the WMO-800S radio modem is relatively simple. As data is received at the
serial port, the data is transmitted on the radio channel. Up to 530 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
530 bytes). If more than 530 bytes is input, the WMO-800S unit will transmit the first 530
bytes; then the next 530 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 2Kbytes is provided. The RS232 connection provides CTS control to prevent the
buffer overflowing. There are no data flow control signals for RS485.
A radio channel cannot provide as secure a data channel as a wired connection. The WMO-
800S uses a radio band with a low level of natural or industrial noise, however there is a
chance of interference from other users of the unlicensed 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 WMO-800S modules. The modules may be configured by the user to
operate in one of two modes. In transparent mode, it is assumed that the host devices control
the flow of data. In controlled mode, the WMO-800S units control the flow of data.
1.2 Transparent Mode
The default configuration of the WMO-
800S modem is transparent mode - the
modules are set in this mode at the factory.
In transparent mode, the WMO-800S
provides no control of the data
transmissions (no error correction). Input
data is simply transmitted by radio and
every other WMO-800S unit in that system
which receives the transmission will output
the data. This mode relies on the host
devices to perform the “handshaking”
function, and re-transmitting serial data if the data is corrupted (no “handshake”). It also
relies on the host devices to include any addressing necessary in the data. In this mode,
modules are not configured with a unit address. Data is “broadcast” - every other WMO-
800S in the system will receive the data and output the data to their individual host devices.
The user may configure the WMO-800S modems to add error checking to each data packet
transmitted - if error checking is configured, data will not be output if it is received without a
correct error-check. This feature provides additional protection against corruption of the data
during the radio transmission. If error-checking is not configured, then the data received by
radio will be output without checking for errors.
HOST
800S
DATA
HOST
800S
DATA
HOST
800S
DATA
User Manual
INM WMO800S_v1.8.doc Page 9
Transparent mode is “point-to-multipoint” communications, suitable for a host device which
is able to communicate on a multi-drop “bus” type network. An example of an application is
the use of radio modems to extend a PLC RS485 network. The serial messages from the
PLC’s already include PLC addressing and error detection/correction to control the flow of
data.
1.3 Controlled Mode
“Controlled mode” provides “point-to-
point” communications similar to telephone
modems. In controlled mode, the flow of
data is controlled by the WMO-800S units.
Each WMO-800S unit is configured with an
address by the user, and a destination
address for the data to be transmitted to.
Data is transmitted addressed to the
destination module, and only this module
will output the serial data. The source
module will add an error-check (16 bit
CRC) to the data transmitted by radio. The destination module will process the error-check,
and if correct, it will transmit an acknowledgment message (ACK) back to the source
module. If the source module does not receive a ACK, it will re-transmit the data. The
source module will attempt to transmit the data up to five times, until an acknowledgment
(ACK) is received. If an acknowledgment is still not received, then the DCD signal on the
RS232 port will be reset and a alarm message can be sent to the host via the serial port.
An example of an application using controlled mode would be a radio modem link between
an intelligent gas analyser and a monitoring computer system. Intelligent transducers do not
normally provide addressing or error checking functions - these would be provided by the
WMO-800S modules.
In controlled mode, the destination address may be pre-set, or set on-line by the host device
using “Hayes” commands. Hayes commands are a standard set of commands used with
conventional telephone modems. An example of an application that would use Hayes
command to set destination addresses would be a central computer polling data loggers for
periodic information.
PLC
800S
800S
RS485
PLC
PLC
800S
PLC
HOST
800S
DATA
HOST
800S
NO DATA
HOST
800S
DATA
#1 #2
#3
WMO-800S Radio Modem Module
Page 10 June 2010
1.4 Repeater Units
A WMO-800S unit may be used as a repeater to re-transmit radio messages. The purpose of
a repeater unit is to extend radio range.
In transparent mode, there can be an unlimited number of repeaters, however with some
conditions (refer to Section 3.5).
The repeater in transparent mode will repeat every transmission it receives.
In controlled mode, up to five repeaters may be configured for any transmission path. The
repeaters are configured by address.
PLC
800S
800S
RS485
PLC
PLC
800S
PLC
REPEATER
800S 800S 800S 800S
800S 800S 800S 800S
User Manual
INM WMO800S_v1.8.doc Page 11
Chapter Two INSTALLATION
2.1 General
The WMO-800S module is housed in a rugged aluminium case, suitable for DIN-rail
mounting. Terminals will accept wires up to 2.5 sq mm in size.
Normal 110-240V mains supply should not be connected to any terminal of the WMO-
800S module. Refer to Section 2.3 Power Supply.
Before installing a new system, it is preferable to bench test the complete system.
Configuration problems are easier to recognize when the system units are adjacent.
Following installation, the most common problem is poor communications caused by
incorrectly installed antennas, or radio interference on the same channel, or the radio path
being inadequate. If the radio path is a problem (i.e. the path is too long, or obstructions are
in the way), then higher performance antennas or a higher mounting point for the antenna
may rectify the problem. Alternately, use an intermediate WMO-800S module as a repeater.
The foldout sheet WMO-800S Installation Guide provides an installation drawing
appropriate to most applications. Further information is detailed below.
Each WMO-800S module should be effectively earthed via the "GND" terminal on the
module - this is to ensure that the surge protection circuits inside the WMO-800S module are
effective.
2.2 Antenna Installation
The WMO-800S module will operate reliably over large distances. The distance which may
be reliably achieved will vary with each application - depending on the type and location of
antennas, the degree of radio interference, and obstructions (such as hills or trees) to the radio
path. The expected range for radio data rates of 19200 bits/sec is 5 km line-of-sight . At
38400 bit/sec, the expected distance will be approx 3 km, and at 76800, the distance will be
1.5 km.
Where it is not possible to achieve reliable communications between two WMO-800S
modules, then a third WMO-800S module may be used to receive the message and re-
transmit it. This module is referred to as a repeater.
An antenna must be connected to each WMO-800S module using the female SMA connector
at the top of the module.
To achieve the maximum transmission distance, the antennas should be raised above
intermediate obstructions such that the radio path is true “line of sight”. Because of the
curvature of the earth, the antennas will need to be elevated at least 5 metres above ground
for paths of 5 km. For short distances, the modules will operate reliably with some
obstruction of the radio path. Obstructions which are close to either antenna will have more
of a blocking effect than obstructions in the middle of the radio path. For example, a group
of trees around the antenna is a large obstruction, and the antenna should be raised above the
trees. However if there is at least 100 metres of clear path before a group of trees, the trees
will have less affect on the radio path.
The modules provide test diagnostics to test the radio path and display radio signal strength.
WMO-800S Radio Modem Module
Page 12 June 2010
An antenna should be connected to the module via 50 ohm coaxial cable (eg RG58, Cellfoil
or RG213) terminated with a male SMA connector. The higher the antenna is mounted, the
greater the transmission range will be, however as the length of coaxial cable increases so do
cable losses. For use on unlicensed frequency channels, there are several types of antennas
suitable for use. It is important antennas are chosen carefully to avoid contravening the
maximum power limit on the unlicensed channel - if in doubt refer to an authorized service
provider.
The maximum net gain of the antenna/cable configuration permitted is 0dB.
The gains and losses of typical antennas are:
Antenna Gain (dB)
Dipole with integral 15’ cable 0
5dBi Collinear (3dBd) 5
8dBi Collinear (6dBd) 8
6 element Yagi 10
9 element Yagi 12
16 element Yagi 15
Cable type Loss (dB per 30 ft / 10 m)
RG58 -5
RG213 -2.5
Cellfoil -3
The net gain of the antenna/cable configuration is determined by adding the antenna gain and
the cable loss. For example, a 6 element Yagi with 70 feet (20 metres) of Cellfoil has a net
gain of 4dB (10dB – 6dB).
The net gain of the antenna/cable configuration is determined by adding the antenna gain and
the cable loss. For example, a 6 element Yagi with 20 metres of RG58 has a net gain of 0 dB
(10dB – 10dB).
Connections between the antenna and coaxial cable should be carefully taped to prevent
ingress of moisture. Moisture ingress in the coaxial cable is a common cause for problems
with radio systems, as it greatly increases the radio losses. We recommend that the
connection be taped with a layer of PVC insulating tape, then a layer of vulcanizing tape such
as “3M 23 tape”, with a final layer of PVC insulating tape.
Where antennas are mounted on elevated masts, the masts should be effectively earthed to
avoid lightning surges. Although the WMO-800S module is fitted with surge protection,
additional surge suppression devices are recommended if lightning surge problems are
experienced. If the antenna is not already shielded from lightning strike by an adjacent
earthed structure, a lightning rod may be installed above the antenna to provide shielding.
2.2.1 3dB/6dB Collinear antenna.
A collinear antenna transmits the same amount of radio power in all directions - as such that
are easy to install and use. For marginal radio paths, the following lengths are the
recommended maximum for the coaxial cable to the antenna. RG58 -10 metres, RG213 - 20
metres. Note that this applies to marginal paths only - if the radio path has a strong radio
User Manual
INM WMO800S_v1.8.doc Page 13
signal, then longer lengths of cable (and hence more cable loss) can be tolerated. If more
than 20 metres of cable is required for a marginal path installation, then a low loss cable such
as 10D-FB, or a higher gain antenna should be used. Collinear antennas should be mounted
vertically, at least 1 metre away from a wall or mast.
2.2.2 Yagi antennas.
A Yagi antenna provides high
gain in the forward direction,
but lower gain in other
directions. This may be used
to compensate for coaxial cable
loss for installations with
marginal radio path.
The Yagi gain also acts on the
receiver, so adding Yagi
antennas at both ends of a link
provides a double improvement.
Yagi antennas are directional.
That is, they have positive gain
to the front of the antenna, but
negative gain in other
directions. Hence Yagi
antennas should be installed
with the central beam
horizontal and must be pointed
800S
Antenna installed
with drain holes
down
Coax feed
loo
p
ed
90
o
1m minimum
COLINEAR
ANTENNA
MAST
EARTH STAKE
IF GROUND CONDITIONS ARE
POOR, INSTALL MORE THAN
ONE STAKE
INSTALL AERIAL ABOVE
LOCAL OBSTRUCTIONS
ANT
800S
SURGE
ARRESTOR
(OPTIONAL) COAXIAL CABLE
WEATHERPROOF
CONNECTORS WITH
“3M 23” TAPE
STRESS RELIEF LOOP
PROVIDE GOOD
GROUND
CONNECTION TO
MAST, MODULE
AND SURGE
ARRESTOR
GND
WMO-800S Radio Modem Module
Page 14 June 2010
exactly in the direction of transmission to benefit from the gain of the antenna. The Yagi
antennas may be installed with the elements in a vertical plane (vertically polarized) or in a
horizontal plane (horizontally polarized). For a two station installation, with both modules
using Yagi antennas, horizontal polarization is recommended. If there are more than two
stations transmitting to a common station, then the Yagi antennas should have vertical
polarization, and the common (or “central” station should have a collinear (non-directional)
antenna.
Also note that Yagi antennas normally have a drain hole on the folded element - the drain
hole should be located on the bottom of the installed antenna.
2.3 Power Supply
The WMO-800S module is powered from a 10 - 30VDC or 13 – 24VAC supply, minimum 9
Watt capacity.
For DC supplies, the negative side of the
supply is connected to "COM" and may be
connected to “ground”. The supply negative
is connected to the “GND” terminal internally.
The positive side of the supply must not be
connected to earth. The DC supply may be a
floating supply or negatively grounded.
The power requirements of the WMO-800S
units is 80mA at 12VDC or 50mA at 24VDC.
The power requirements in low power mode is
20mA at 12VDC.
2.4 Serial Connections
2.4.1 RS232 Serial Port
The serial port is a 9 pin DB9 female and provides for connection to a host device as well as
a PC terminal for configuration, field testing and for factory testing. This port is internally
shared with the RS485 - ensure that the RS485 is disconnected before attempting to use the
RS232 port. Communication is via standard RS232 signals. The WMO-800S is configured
as DCE equipment with the pin-out detailed below.
Hardware handshaking using the CTS/RTS lines is provided. The CTS/RTS lines may be
used to reflect the status of the local unit’s input buffer, or may be configured to reflect the
status of CTS/RTS lines at the remote site. The WMO-800S does not support XON/XOFF.
Example cable drawings for connection to a DTE host (a PC) or another DCE host (or modem)
are detailed below.
800S
10 – 30 +
VDC -
+
-
800S
13 - 24
VAC
+
-
User Manual
INM WMO800S_v1.8.doc Page 15
DB9 Connector Pinout
Pin Name Direction Function
1 DCD Out Data carrier detect –
- driven when link is established in controlled mode
- driven always in transparent mode
2 RD Out Transmit Data – Serial Data Output
3 TD In Receive Data – Serial Data Input
4 DTR In Data Terminal Ready - DTR can be configured to initiate low power
mode, or to force a link disconnection (“hang up” in controlled mode.
5 SG Signal Ground
6 DSR Out Data Set Ready - always high when unit is powered on.
7 RTS In Request to Send - hardware flow control configurable
8 CTS Out Clear to send - hardware flow control configurable
9 RI Ring indicator - indicates another module is attempting to connect in
controlled mode.
800S
DB9
MALE
DTE HOST
DB9
FEMALE
800S
DB9
MALE
DCE HOST
DB9
MALE
2.4.2 RS485 Serial Port
The RS485 port provides for communication between the WMO-800S unit and its host device
using a multi-drop cable. Up to 32 devices may be connected in each multi-drop network. Note
that the RS485 port is shared internally with the RS232 port - make sure that the RS232 port is
disconnected before using the RS485 port.
As the RS485 communication medium is shared, only one of the units on the RS485 cable
may send data at any one time. Thus communication protocols based on the RS-485 standard
require some type of arbitration.
RS485 is a balanced, differential standard but it is recommended that shielded, twisted pair
cable be used to interconnect modules to reduce potential RFI. It is important to maintain the
polarity of the two RS485 wires. An RS485 network should be wired as indicated in the
diagram below and terminated at each end of the network with a 120 ohm resistor. On-board
120 ohm resistors are provided and may be engaged by operating the single DIP switch in the
end plate next to the RS485 terminals. The DIP switch should be in the “1” or “on” position
to connect the resistor. If the module is not at one end of the RS485 cable, the switch should
be off.
WMO-800S Radio Modem Module
Page 16 June 2010
HOST WMO-800S HOST
RS485 CONNECTIONS
User Manual
INM WMO800S_v1.8.doc Page 17
Chapter Three OPERATION
3.1 Power-up and Normal Operation
When power is initially connected to the WMO-800S module, the module will perform
internal diagnostics to check its functions. The following table details the status of the
indicating LEDs on the front panel under normal operating conditions.
LED Indicator Condition Meaning
OK On Normal Operation
Radio RX GREEN flash
RED flash
Radio receiving data
Weak radio signal
Radio TX Flash Radio Transmitting
Serial RX GREEN flash
RED flash
Serial Port Receiving
CTS low
Serial TX GREEN flash Serial Port Transmitting
DCD On Transparent mode - always on
Controlled mode - on when
communications link is established
DCD Off Communications failure or link not
established
Other conditions indicating a fault are described in Chapter Six Troubleshooting.
3.2 Serial and Radio Data
The WMO-800S module provides a full-duplex RS232 serial port and half-duplex RS485
serial port - only one serial port can be used at any one time. The radio communications is
half-duplex - this means that the WMO-800S operates at half duplex. Many applications use
full duplex RS232 communications but do not require full duplex - the protocol used operates
at half-duplex and will operate with the WMO-800S without problems. If an application
really requires full duplex communications, then the WMO-800S should not be used.
Data input at the serial port is placed into the input buffer. This buffer will store 2Kbytes of
data, and CTS/RTS control can be configured on the RS232 port to prevent overflow.
When the WMO-800S unit detects data in the input buffer, it initiates a radio message. The
radio message will end when the number of transmitted bytes reaches the maximum message
length (configurable by the user), or if the input buffer becomes empty.
WMO-800S Radio Modem Module
Page 18 June 2010
If the configured serial data rate is the same or more than the radio data rate, then data is
transmitted as soon as it enters the input buffer - data “streams” from the input buffer to the
radio port. If the serial rate is less than the radio rate, then the transmission will be delayed
for a period to allow sufficient data to build up in the input buffer to avoid the radio emptying
the input buffer before a complete serial message has been input. The WMO-800S will
calculate the amount of delay depending on the difference between the serial and radio rates.
The radio transmission will stop when the input buffer is empty or when the radio has
transmitted the maximum number of bytes (user configurable - maximum 530 bytes). If there
is still data in the input buffer, the WMO-800S will start another radio transmission.
If error checking is configured, then a 16 bit CRC error-check is added to the end of the
transmitted data packet. The receiving module will receive the full data packet and check the
CRC before outputting the data.
The maximum size of the data packet is configurable by the user (maximum is 530 bytes). If
the data input to the WMO-800S is less than the maximum size, then the WMO-800S will
transmit the actual data input. If the data exceeds the maximum packet size, then the WMO-
800S will transmit multiple packets until all of the data is transmitted.
Because of radio start-up delays, the effective radio data rate will be lower than the
transmitted data rate. If you are sending large blocks of data, and the serial rate is equal or
more than the radio rate, we recommend that you use CTS/RTS flow control to prevent the
input buffer from overflowing.
3.2.1 Character Type
The WMO-800S may be configured by the user to recognize the following types of
characters - 7 or 8 data bits, even or odd or no parity, 1 or 2 stop bits.
Most applications will require the character type to be the same at each WMO-800S modem
in the system. Nevertheless, the character type may be configured to be different at different
WMO-800S modems. Data is transmitted by radio as an eight-bit byte without stop or start
bits. If the input data is 7 data bits, then the byte transmitted by radio comprises the 7 bits
plus a zero bit. Input characters with 8 bits are transmitted as just the 8 data bits, with no
parity. Because the data is transmitted without parity, the user may configure CRC error
checking to be added to each transmitted data packet. Data is output at the destination
module based on the character type configured at that module - that is, the start/stop bits and
parity is added to the radio data.
3.2.2 Serial Data Rate
The communications baud rates supported on both the RS232 serial port and the RS485 serial
port are 1200, 2400, 4800, 9600, 14400, 19200, 28800, 31250, 38400, 57600, 76800 and 115200
baud - the user selects one of these rates during the configuration of the modem.
3.2.3 Radio Data Rate
The data is transmitted by radio as direct modulated synchronous data at 19200, 38400 or
76800 bits/second. The user must configure the radio data rate at each WMO-800S module.
The configured radio data rates must be the same for each module in a system.
At 19200 and 38400 bits/sec, the WMO-800S adds forward error correction in the
transmitted data. This is added automatically and is different to the configurable CRC error-
check.. The radio range at 19200 baud is better than 38400 or 76800. The expected range at
38400 is 60% of maximum and at 76800 is 30%.
User Manual
INM WMO800S_v1.8.doc Page 19
The radio message includes the following :-
A 5 - 10 msec leading sequence of alternating 1’s and 0’s provides the receiving unit
with time to capture and lock onto the incoming signal.
A system address is superimposed on each message to provide discrimination
between different WMO-800S systems on the same radio channel. Each WMO-800S unit in
the same system must be configured with the same system address - refer Section 4,
Configuration. Although other WMO-800S modules may hear the radio transmissions,
because they have a different system address, the radio transmission is ignored and no serial
data is output.
In transparent mode, a group address is included, and in controlled mode, unit
addressing is included.
An error-check (16 bit CRC) may be configured by the user.
Up to 530 bytes of data may be transmitted in a message - the maximum message size is
configurable between 10 and 530 bytes. The data consists of a sequence of 8 bit bytes. Start,
stop and parity bits are not transmitted, but they are re-generated at the receiving unit (if
configured).
A “transmit delay” time and a “receive delay” time may also be configured. These parameters
may be used to fine tune and give priority to different WMO-800S units in a system.
After each message is transmitted, a WMO-800S unit will not transmit another message
during the transmit delay time. This could be used to allow a reply message to be received
before the next message is sent.
After a message is received, a message will not be transmitted during the receive delay time.
This could be used to delay a reply message until other messages have been sent.
3.3 Addressing
A WMO-800S network comprises modules with the same "system" address. Only modules
with the same system address will communicate with each other. This feature allows more
than one system to operate in the same area on the same radio channel. We recommend that
you select a random number for the system address.
In transparent mode, each module is also configured with a “group” address. A system may
comprise several groups or sub-systems. Only modules with the same system and group
address will communicate directly with each other - but modules with different group
addresses can communicate via a repeater. The group address is used for repeater operation
in transparent mode. The group address is not used in controlled mode.
A WMO-800S can also be configured with a “unit” address - this gives the module a unique
identification. The unit address feature is not used in transparent mode, but it is used in
controlled mode.
3.4 Transparent Mode
In transparent mode, radio messages are transmitted without unit addressing. Units do not
provide handshaking functions to control the flow of data. Every unit which receives the
WMO-800S Radio Modem Module
Page 20 June 2010
radio message, and has the correct system and group addresses, will output the data.
Transparent mode operation is effectively a broadcast system.
Data received at the serial port is transmitted out of the radio port. Data received from the
radio is transmitted out of the serial port. Prior to transmitting, units will listen to the radio
channel to ensure that it is clear - units will hold off from transmitting until the radio channel
is clear. At the RS232 port, the CTS pin can be configured to go high while there is space in
the input data buffer - otherwise it is always high.
Host devices should provide a suitable protocol to ensure that error checking, handshaking
and implementation of an appropriate re-transmission scheme is provided. This mode of
operation is particularly suited to devices designed to operate over a multidrop network, such
as PLC systems designed for operation over a RS-485 network.
The time taken to transmit a message is :-
lead-in system/group addr data error check (if configured)
|---------------|-----------------|------------------------------------------|--------------|
5 msec 2 bytes 0.5ms per byte 2 bytes
1 ms @19.2Kb @ 19.2Kb 1ms @ 19.2Kb
If error checking is not configured at the receiving unit, data will start to be output
approximately 1 msec after the system address has been received. If error checking is
configured, data will be output approx 2msec after the end of the message. For example, a
message with 20 bytes of data transmitted at 19200 bits/sec will begin to be output approx
12msec after the data is input, if there is no error checking, or 24msec after the data is input if
error checking is configured.
3.5 Transparent Mode Repeaters
A module can be configured as a transparent mode repeater. In this mode, the module will
operate as a normal transparent mode module, plus it will also re-transmit any radio messages
that it receives. However it will change the group address in the re-transmitted message. The
transparent mode repeater is configured with two group addresses. When it receives a radio
message with one of these group addresses, it will re-transmit the message using the other
group address (assuming that the system address is correct).
One of the group addresses will be its normal or “first” group address. If a transparent mode
repeater receives a message on its first group address, it will output the data on its serial port,
and will also re-transmit the message using its second group address. That is, the re-
transmitted message will now have the second group address. Only WMO-800S modules
configured with the second group address will accept the re-transmitted message.
If a transparent mode repeater receives a message on its second group address, it will re-
transmit the message on its first group address, but it will not output the data on its serial
port.
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