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TDM2
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The TDM2 is a very simple 433MHz band
radio data modem. It provides a medium ranged half duplex,
transparent data link between a pair of 9600 baud RS232
ports without any additional interface circuitry.
The TDM2 is a TDL2A radio module, combined
with suitable interface circuits, power supplies and connectors,
packaged in an attractive instrument case. In the simplest
case, a pair of 'box modems' (with suitable aerials and
power supplies connected, of course) can be connected directly
to the serial ports of a pair of industrial PCs and the
resulting wireless data link used without any further installation
or programming.
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Figure 1: TDM2-433-9 |
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RS232 driver
and DB9F connector for direct interface to PC serial
port
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Serial modem
baud rate at 9600bps (half-duplex)
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Addressable
point-to-point
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5 serial select
wideband channels (in the 433.05 - 434.79MHz European
band)
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Access to internal
diagnostic/Test modes using HyperTerminal
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On board SMA
antenna connector
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Signal LED for
visual indication of valid code received
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Setup is simple
as Plug-and-Play
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Set-up and configuration
using HyperTerminal
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Conforms to
EN 300 220-3 and EN 301 489-3
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Size: 94 x 107
x 33mm (excluding connectors)
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Handheld / portable
terminals
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PDAs, organisers &
laptops
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Industrial telemetry
and telecommand
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In-building environmental
monitoring and control
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Remote data acquisition
system, data logging
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Fleet management,
vehicle data acquisition
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Figure 2: TDM2 (rear view) |
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Looked at from the outside, the TDM2
presents:
| Part |
Function |
Position |
| 9 way D-type |
RS232 port |
rear of the case |
| SMA RF connector |
Aerial |
rear of the case |
| 2.1mm power jack |
External power (9-15v) |
rear of the case |
| 4 way DIP switch |
Mode selection (see
later) |
rear of the case |
| Slide switch |
Internal battery 'on/off' |
in a recess, on the
side of the case |
| Three LED indicators |
Power on |
green, on the left |
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Valid data receiving |
red, in the middle |
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Transmitting |
(red, on the right) |
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Powering the TDM
The TDM2 radio modem requires
a source of energy to operate. There are several options:
- External
supply: The TDM unit is intended to be supplied
from a 9-15v DC supply (6-15v if the internal battery
is not fitted). The basic unit requires up to 50mA,
plus any extra current drain from the +5v output (pin
9 on the D-type). The supply can be fed in through the
2.1mm power jack (positive to centre connector) or through
pin 1 of the 9 way D connector.
- Local +5v:
The user may also power the unit by applying a regulated
+5v supply to pin 9 of the D-type. In this mode of operation
the internal battery must be removed, and switch 2 set
to 'on'. The supply must be clean, and ripple free,
as this mode of operation bypasses the internal supply
regulator
- There is
provision for an internal PP3 battery: This is
intended as a backup power source, and for use during
experimentation and set-up. A standard, high capacity
alkaline battery will provide around 15 hours of continuous
operation. (The use of rechargable batteries in this
unit is not recommended at this time)
The internal battery is enabled by
the recessed slide switch on the right of the case (slide
switch backwards to enable the battery. To change the
battery, the unit must be dis-assembled by removing the
polymer 'feet' and removing the four assembly screws.
The battery is retained to the pcb by a standard 'tie
wrap'.
When an external supply exceeding 9v
is fed to the unit (through the power jack or the D connector),
the internal battery is not used (there are steering diodes
in series with both power sources)
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Connecting the TDM
This unit is connected to an
RS232 serial port via a standard 9 way D connector. True
(bipolar) RS232 levels are provided by this interface.
The interface provides TXD/RXD, plus a basic CTS function
(indicating that the radio is busy receiving a data burst).
Other pins are used for functions specific to the TDM
(mode and standby, power supplies).
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Figure 3: TDM2 DB9 Serial Port
pin outs |
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| Serial interface
The TDM2 serial interface operates
at 9600 baud only, with 1 start, 8 data and 1 or 2 stop
bits.
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| Pin |
Name |
Function |
| 1 |
Vcc |
Raw supply voltage
input (9-15v. ) |
| 2 |
RXD |
RS232 data out |
| 3 |
TXD |
RS232 data in |
| 4 |
DTR |
Pull low to disable
unit. (Pin function enabled by switch 1) |
| 5 |
0V |
Supply ground |
| 6 |
PGM |
Pull low to enter
program mode. (Pin function enabled by switch 4) |
| 7 |
N/C |
No connection |
| 8 |
CTS |
Low = Unit has valid
data in rx buffer |
| 9 |
+5V out |
Regulated supply output.
200mA max. (independent of DTR switching) (Pin function
enabled by switch 2) |
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Notes:
1. Pins 4 and 6 have internal
pullups to +5v, pin 3 has a pulldown to 0V
2. All ' Input' pins (3,4,6) will tolerate true +/-
RS232 levels. No extra buffering is required.
3. The RX_busy (CTS, pin 8) circuitry incorporates a
pulse lengthening monostable, to eliminate the strobing
or 'flashing' seen with TDL2A modules during streaming
data, as the buffer fills and empties.
4. A simple addressing structure is included in the
datastream. Units may be programmed onto one of eight
addresses (all units are supplied set to default addr=0)
5. A version is available in a robust extruded aluminium
housing. Contact Radiometrix Sales for details
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| Don't
forget the aerial: The TDM2
is a wireless device, and will not function without a suitable
aerial. The supplied part (a high quality 433MHz band helical
type) is attached to the SMA connector on the rear of the
casing. Use sufficient (but not excessive) torque to tighten
the screw collar. Finger-tight is correct.
Alternative aerials may be connected
to this connector via a length of RF coax. Contact technical
support for advice.
A good first
demonstration can be had by:
- Set up
a pair of PCs, with serial (RS232) ports.
Connect them together with a null modem (pins 2/3 swap
over) cable.
- Run terminal emulator (ie: Hyperterminal)
programs on both computers. (Port settings 9600 baud,
1+8+1, local echo)
- At this point you have a simple
'teletype' link between the machines. Anything typed
on one is seen on the other.
- Now replace the null modem cable
with a pair of TDM2 radio modems. You will see no change.
The radio link seamlessly replaces the cable
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Configuring the interface: A
4 way DIP switch is located in a recess on the rear of
the case. As supplied, all switches are 'off' ('up').
These switches control certain interface functions.
Switches
| SW No. |
Name |
Function |
| 1 |
DTR EN |
Switch 'on' to enable
pin 4 switching (otherwise unit is always on) |
| 2 |
+5v/pin 9 |
Switch 'on' to enable
the +5v external supply pin |
| 3 |
Setup |
Switch 'on' to force
unit into setup/program mode |
| 4 |
Ext setup en |
Switch 'on' to enable
pin 6 (N_PGM) |
Indictors
| SW No. |
Position |
Function |
| 1. Power |
Green, on the left |
Unit is powered when
lit |
| 2. Transmit |
Red, in the centre |
When lit, the unit's
transmitter is on, and it is sending a data packet |
| 3. Receive |
Red, on the right |
When lit, the unit
has received a valid data packet, and is outputting
it |
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NOTES:
- It ought
to be emphasised that the TDM2 is a very simple, easy
to use, device. It is also relatively unsophisticated.
The data rate is limited to 9600 baud, the link is half
duplex, and although there is a simple addressing structure,
there is no provision for extensive data buffering,
FEC, or acknowledge/re-transmit error handling protocols.
Inside the box, the TDM2 is simply a TDL2A radio module
with necessary interface circuits, power supplies and
connectors.
- The TDM2
provides a half duplex link: Provided no two devices
attempt to transmit at one time (a 'low' on RX_busy
may be used as a primitive 'CTS' indication) no further
restrictions on data transmission need be made, as all
transmit timing, valid data identification and datastream
buffering is conducted by the unit. There is no 'transmit
enable' pin. Sync and framing words in the packet prevent
the receiver outputting garbage in the absence of signal
or presence of interference.
- At the edge of it's range, or in
the presence of other interferers, there will be packets
(of 1-3 bytes each) lost, or occasionally corrupted.
If a greater degree of data fidelity is needed, then
the user ought to introduce another layer of data handling.
In our own tests we have used the Z-modem file transfer
protocol with great success. In simpler, control type,
applications these data errors will be of lesser significance.
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| Configuring
the TDM2
In order to use all the functions embedded
in the on board TDL2A modem, the user must be aware of
the setup /programming facility, which allow different
addresses and frequency channels to be set up, and if
necessary accesses diagnostic test modes.
As supplied, the TDM2 is set to address
zero, and channel zero. To change these presets, it is
necessary to enter setup/program mode.
The TDM2 is programmed through the
same RS232 port that is used for sending/receiving data.
An RS232 terminal emulator (such as Aterm or HyperTerminal)
is an ideal tool.
To enter program mode either switch
3 is temporarily turned 'on', or pin 6 of the D connector
is pulled low (providing switch 4 is 'on'). In this mode
the radio link is disabled, but characters sent (at 9600
baud, as normal) to the unit are echoed back on the RXD
pin.
Connect the TDM2 to the PC serial port
using a serial straight through cable.
The HyperTerminal should be set
with the following settings.
9600 baud RS232, 8 bit data, no parity, 1 start bit, 1
or 2 stop bits. No flow control.
The unit will
only respond to certain command strings:
| ADDR0
to ADDR7 <CR> |
These commands set up one of 8 unique addresses.
A TDL2A will only communicate with a unit set to
the same address.
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| CHAN0
to CHAN4 <CR> |
These commands select
one of 5 preset channels |
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A TDL2A will only communicate with a unit set to
the same address and the same channel.
Address and channel numbers are stored in volatile
memory. On power-up the TDL2A reverts to the default
in EEPROM (as supplied this is always address 0
and Channel 0)
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| SETPROGRAM <CR>
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Writes the current
set address into EEPROM as the new default.
A tilda character (~, ascii 126dec) sent by the unit
indicates end of EEPROM write sequence |
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normally only used for factory diagnostics) |
| NOTONE <CR> |
Transmit unmodulated
carrier |
| LFTONE <CR>
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Transmit carrier modulated
with 8KHz squarewave |
| HFTONE <CR>
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Transmit carrier modulated
with 16KHz squarewave |
| # <CR>
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Transmitter
off |
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| A Carriage Return
'<CR>' (00Dhex) should be entered after each
command sequence to execute it. |
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| Releasing the 'setup'
pin to high state (or turning off switch 3) returns
the unit to normal operation |
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Condensed specifications
| Frequency |
433.925MHz - CHAN0
(default channel) |
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433.285MHz - CHAN1 |
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433.605MHz - CHAN2 |
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434.245MHz - CHAN3 |
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434.565MHz - CHAN4 |
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Frequency
stability
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+/- 10kHz |
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Channel
width
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320kHz |
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Number
of channels
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1 of 5, user programmed |
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Supply voltage
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5V |
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Current
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28mA transmit |
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22mA receive/idle
(plus up to 10mA in to RS232 port)
20uA disabled |
| Operating temperature |
-20 to +70 °C
(Storage -30 to +70 °C) |
| Size |
94 x 107 x 33 mm (excluding
connectors)
The case is an ergonomic ABS moulding, designed by
HCPA version is available in a robust extruded aluminium
housing. Contact Radiometrix Sales for details |
| Spurious radiations |
Compliant with ETSI
EN 300 220-3 and EN 301 489-3 |
| Interface user |
9pin D type |
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Power |
2.1mm connector |
| Mode |
4 position DIP switch |
| RF |
SMA |
| Indicators |
Power on (green LED)
Sending (red LED)
Receiving (red LED) |
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| Transmitter
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| Output power |
10dBm (10mW) ±1dB(A
25mW (+14dBm) power output AUS/NZ version is available) |
| TX on switching
time |
<4 ms |
| Modulation
type |
16kbps
bi-phase FSK |
| FM peak
deviation |
+/-25kHz
(nominal) |
| Adjacent channel TX
power |
<-37dBm |
| TX spurious |
<-45dBm |
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| Receiver |
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| Sensitivity |
-105dBm
for 1% BER |
| image |
-40dB |
| spurious / adjacent
channel |
-60dBm |
| blocking |
-80dB nominal, 75dB
worst case |
| LO re-radiation |
<-60dBm |
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| Modem |
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| Baud rate |
9600baud (transparent,
half duplex)(a 4800 baud version, TDM2-433-4 , is
available to special order) |
| Format |
1 start, 8 data, 1
stop, no parity |
| Radio channel data
rate |
16kbps peak |
| Coding |
Biphase |
| Packet length |
3 bytes |
| Buffers |
32 byte FIFO |
| Flow control |
None ('RX busy' pin
provided) |
| Addressing |
1 of 8, user programmed |
| Data latency |
14ms (first
byte into TX to first byte out of RX) |
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Limitation of liability
The information furnished by Radiometrix Ltd is believed
to be accurate and reliable. Radiometrix Ltd reserves
the right to make changes or improvements in the design,
specification or manufacture of its subassembly products
without notice. Radiometrix Ltd does not assume any liability
arising from the application or use of any product or
circuit described herein, nor for any infringements of
patents or other rights of third parties which may result
from the use of its products. This data sheet neither
states nor implies warranty of any kind, including fitness
for any particular application. These radio devices may
be subject to radio interference and may not function
as intended if interference is present. We do NOT recommend
their use for life critical applications.
The Intrastat commodity code for all our modules is: 8542
6000.
R&TTE Directive
After 7 April 2001 the manufacturer can only place finished
product on the market under the provisions of the R&TTE
Directive. Equipment within the scope of the R&TTE
Directive may demonstrate compliance to the essential
requirements specified in Article 3 of the Directive,
as appropriate to the particular equipment.
Further details are available on The Office of Communications
(Ofcom) web site:
Licensing
policy manual
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