Data Sheet

Hartcran House, 231 Kenton Lane, Harrow, Middlesex, HA3 8RP, England
Tel: +44 (0) 20 8909 9595, Fax: +44 (0) 20 8909 2233,
Issue 1, 15 September 2015
2700 baud wireless packet modem
The CPX2s a 2,700 baud half-duplex serial radio
packet modem module operating on licenceexempt European 433.05-434.79MHz SRD band.
CPX2 is an intermediate level OEM radio
modem which is in between a raw FSK radio
module like BiM2G and a sophisticated OEM
radio modem like RPM2A. It takes care of
preamble, frame synchronisation and error
Figure 1: CPX2-433.92-2k7
Conforms to EN 300 220-2 and EN 301 489-3
SAW front-end filter
Small size
Low cost
Direct interface to microcontroller UART
Serial modem baud rate at 2,700bps (half-duplex)
200m line of sight operating range
Home/Industrial Automation
Vehicle Sensor Monitoring
Data Logging Systems
Security Systems for Home/Industrial
In-building environmental monitoring and control
Sports and Performance Monitoring
Technical Summary
Operating frequency: 433.92MHz (default)
Modulation: 2.7kbps NRZ FSK
UART interface: 57,600bps, 8 data bits, Parity None, Flow Control None
Supply: 3.3V at 23mA transmit, 13mA receive and <2mA standby
Transmit power: +3dBm (2mW)
Receiver sensitivity: -105dBm (for 0.1% data error)
32 byte data buffer
40 x 14 x 5mm
Radiometrix Ltd
CPX2 Data Sheet
page 1
Figure 2: CPX2 block diagram
Radiometrix Ltd
CPX2 Data Sheet
page 2
Operation of the CPX2 packet data transceiver
The CPX2 is a variant of the basic CLX2 data link device, using the same hardware but achieving
considerably greater range (albeit at the cost of a lower aggregate data rate). On the other hand, Its user
interface data rate is considerably faster (57,600 baud) to minimise data transfer time overhead to and from
the module, so in some applications the CPX2 will actually exhibit better efficiency.
While a standard CLX2 will reliably receive a -95dBm signal, the CPX2 is reliably seen to recover packets at
signal levels of -105dBm and less (corresponding to around twice the range).
The CPX2 is not a transparent modem. It cannot handle constant streaming data.
All timing and data formatting tasks are handled by the software. The user need not worry about keying the
transmitter before sending data. For transmission across the radio link data is formatted into packets, each
comprising data bytes, preamble sequence, frame synchronisation code and checksum.
It sends its data in discrete 32 byte blocks, and while it is sending a block it cannot do anything else.
A 32 byte block (or "packet") takes about 150ms to send (during which the RF carrier is 'on' for 140ms)
The unit idles in receive. If a valid RF packet is detected, then it is immediately decoded and outputted as a
stream of serial data bytes (start bit following preceding stop bit)
If data is presented to a unit's TXD pin, the first byte received initiates the transmit process. The unit will
immediately switch its RF circuits from receive to transmit and start loading any available transmit data into
its buffer. It will carry on loading the buffer until either:
1. 32 bytes are received, or
2. A gap of 5ms is seen following a byte.
At this point the unit pulls the active low TXON pin low and begins modulating its carrier (by now stabilised
and at full power) with the coded data packet. Any "extra" bytes beyond the first 32 are discarded.
Once the burst has been transmitted, the transmitter turns off and TXON is returned to the high state.
In the absence of a valid signal, the CPX2 (in idle/receive) uses framer and checksum data to avoid
outputting random garbage. Similarly, at the edge of the range or in the presence of interference the unit will
either output complete, correct data blocks or nothing at all (it is very unlikely to ever output a corrupted
Pulling the /RXOFF pin low (against its internal pull-up) puts the unit into standby (as on the CLX2)
Figure 3: CPX2 footprint (top view)
Radiometrix Ltd
CPX2 Data Sheet
page 3
Pin description
Received Data output at 3V UART (inverted RS232) level
Transmit Data input at 3V UART (inverted RS232) level [No pull-up]
/TXON Active low Transmitter ON indicator Output [Transmit Mode]
/RXOFF Active low Receiver hot Standby Input [Receive Mode]
Open drain, 50k internal pull-up
3.3V DC (externally regulated power supply)
Received Signal Strength Indicator output
(An optional pad for wire connection)
RF in/out (50 impedance)
RF Ground
1. TXD has no internal pull-up. If the unit is used in Receive only mode, tie this pin to VCC
2. VDD must be a clean 3.3V DC regulated supply
3. The STATUS pin. In transmit, this pin pulls low if the device is transmitting a data packet.
On receive it floats high. If pulled low in receive, the unit goes into hot standby (<2mA)
In standby the unit does not receive, but will go into transmit if valid data is presented to TXD.
4. TXD / RXD are inverted RS232 at 3V CMOS levels. To connect to a true RS232 device, inverting
level shifters must be used (e.g. MAX232 type are ideal, but simple NPN transistor switches with
pull-ups often suffice). With typical microcontrollers and UARTs, direct connection is possible.
5. Because CPX2 provides a lower 2,700 baud half duplex radio link with higher 57,600 user baud rate,
no more than 32 bytes should be uploaded at a time. i.e. data cannot be streamed.
6. Provided no two devices attempt to transmit at one time, then no further restrictions on data
transmission need be made, as all transmit timing, valid data identification and data byte buffering is
conducted by the unit. There is no 'transmit enable' pin. Synchronisation and framing words in the
packet prevent the receiver outputting garbage in the absence of signal or presence of interference.
7. A 2.2k resistance is present from RF pin 1a to ground for ESD protection
Radiometrix Ltd
CPX2 Data Sheet
page 4
Condensed specifications
Frequency stability
Channel width
Number of channels
Supply Voltage
Operating temperature
Spurious radiations
Output power
TX on switching time
Modulation type
FM peak deviation
TX spurious
3.3V DC
23mA transmit
13mA receive/
<2mA standby
-20°C to +55°C (Storage -30°C to +70°C)
Compliant with ETSI EN 300 220-2 and EN 301 489-3
5pin 0.1" pitch molex (pin 6 absent)
2pin 0.1" pitch molex
40 x 14 x 5mm
2mW ±1dB
2.7kbps NRZ FSK
+/-30kHz (nominal)
Local Oscillator re-radiation
-105dBm (for 0.1% data error)
-50dB (±1MHz)
Data rate
Flow control
Initial start up
57,600baud, Half duplex
1 Start bit, 8 Data bits, No parity, 1 Stop bit
3V CMOS (inverted RS232 ‘0’=0V, ‘1’=3V)
32 byte FIFO
10ms from power on
Radiometrix Ltd
CPX2 Data Sheet
page 5
Antenna requirements
Three types of integral antenna are recommended and approved for use with the module:
A) Whip
This is a wire, rod ,PCB track or combination connected directly to RF pin of the module.
Optimum total length is 16cm (1/4 wave @ 433MHz). Keep the open circuit (hot) end well
away from metal components to prevent serious de-tuning. Whips are ground plane
sensitive and will benefit from internal 1/4 wave earthed radial(s) if the product is small and
plastic cased
B) Helical
Wire coil, connected directly to RF pin, open circuit at other end. This antenna is very
efficient given it’s small size (20mm x 4mm dia.). The helical is a high Q antenna, trim the
wire length or expand the coil for optimum results. The helical de-tunes badly with proximity
to other conductive objects.
C) Loop
A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and fed
from RF pin at a point 20% from the ground end. Loops have high immunity to proximity detuning.
Ultimate performance
Easy of design set-up
Immunity proximity effects
The antenna choice and position directly controls the system range. Keep it clear of other metal in the
system, particularly the 'hot' end. The best position by far, is sticking out the top of the product. This is often
not desirable for practical/ergonomic reasons thus a compromise may need to be reached. If an internal
antenna must be used, try to keep it away from other metal components, particularly large ones like
transformers, batteries and PCB tracks/earth plane. The space around the antenna is as important as the
antenna itself.
0.5 mm enameled copper wire
close wound on 3.2 mm diameter former
433 MHz = 24 turns
A. Helical antenna
Feed point 15% to 25% of total loop length
track width = 1mm
4 to 10 cm inside area
B. Loop antenna
C. Whip antenna
wire, rod, PCB-track or a combination
of these three
433 MHz = 16.4 cm total from RF pin.
Figure 4: Antenna types
Radiometrix Ltd
CPX2 Data Sheet
page 6
Radiometrix Ltd
Hartcran House
231 Kenton Lane
Harrow, Middlesex
Tel: +44 (0) 20 8909 9595
Fax: +44 (0) 20 8909 2233
[email protected]
Copyright notice
This product data sheet is the original work and copyrighted property of Radiometrix Ltd. Reproduction in
whole or in part must give clear acknowledgement to the copyright owner.
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
Further details are available on The Office of Communications (Ofcom) web site:
Information Requests
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2a Southwark Bridge Road
London SE1 9HA
Tel: +44 (0)20 7981 3000
Fax: +44 (0)20 7981 3333
European Radiocommunications Office (ERO)
Nansensgade 19
DK 1366 Copenhagen
Tel. +45 33896300
Fax +45 33896330
[email protected]