CLX2 Datasheet, PDF (3/6 Pages) Radiometrix Ltd – 19200 baud modem transceiver

The radio / datastream interface
A 32 byte software FIFO is implemented in both the transmit and receive code. At the transmit end this
is used to allow for the transmitter start up time (about 4ms), while on receive it buffers arriving
packets to the constant output data rate. All timing and data formatting tasks are handled by the
software. The user need not worry about keying the transmitter before sending data: the link is entirely
transparent.
For transmission across the radio link data is formatted into packets, each comprising 6 bytes of data, a
preamble sequence, a sync code and a checksum. If less than 6 bytes are in the transmit end FIFO then
a packet is still sent, but idle codes replaces the unused bytes. When the transmit end FIFO is
completely emptied, then the transmitter is keyed off .
Figure 3: CLX2 footprint (top view)
Pin description
Pin
Name
Function
1
GND
Ground
2
RXD
Received Data output at 3V UART (inverted RS232) level
3
TXD
Transmit Data input at 3V UART (inverted RS232) level [No pull-
up]
4
/TXON
/TXON Active low Transmitter ON indicator Output [Transmit
/RXOFF
Mode]
/RXOFF Active low Receiver hot Standby Input [Receive Mode]
Open drain, 50k internal pull-up
5
VDD
3.3V DC (externally regulated power supply)
RSSI
Received Signal Strength Indicator output
(An optional pad for wire connection)
1a
RF
RF in/out (50 impedance)
2a
RFGND
RF Ground
Notes:
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. The CLX2 provides a half duplex link, but 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 datastream 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.
6. A 2.2k resistance is present from RF pin 1a to ground for ESD protection
Radiometrix Ltd
CLX2 Data Sheet
page 3