SP2-433-160 Datasheet, PDF (17/27 Pages) Radiometrix Ltd – UHF SpacePort Transceiver

APPENDIX - A
A Detailed look at the SP2's transceiver interface
The SP2 interfaces to the transceiver using 4 lines :-
TX output
TXD output
Active low enable for the transmitter.
Serial data to be sent.
RX output
RXD input
Active low enable for the receiver.
Received serial data.
note 1 All lines are 5V CMOS levels
note 2 There is no requirement for a carrier/signal detect signal from the transceiver nor for the RXD
output to be muted when no signal is present.
The enable lines - TX & RX
These normally high, active low lines are used to control the transceiver. The SP2 is a half-duplex
controller thus in normal operation the transceiver is either transmitting or receiving or off.
Transmit Data - TXD
TXD is the serial data to the transmitter, it is held low when the transmitter is not enabled. When the
TX is enabled a synchronous 160kbit/s (6.25µs/bit) serial code is present to modulate the transmitter.
Receive Data - RXD
RXD is a hi-impedance input which is fed with a 'squared-up' (5V logic level) signal from the receivers'
data slicer. The SP2 contains a very selective, noise immune signal detector and therefor does not
require that the RXD signal be muted in the absence of signal, i.e.. squared-up channel noise may be fed
to the SP2 when no signal is present.
The SP2's Packet Encoder
The packet is made-up of 4 parts:
Preamble
This is a simple 80kHz square wave, the number of cycles being programmed by address 01h of the
EEPROM. The preamble has two functions, the initial portion it is used to allow the data slicer in a
remote receiver to establish the correct slicing point (for the BiM2-433-160 this takes a maximum of
0.8ms), after the receiver has settled, the remaining portion is used by the receiving SP2 to positively
identify and phase lock onto the incoming the signal (this requires 12 cycles of preamble). The preamble
may extended to wake-up a remote SP2 in power saving mode.
Frame sync
A 7 bit Barker sequence is used to identify the start of the data. Alternatively if the transmitter is
sending extended preamble (to wake a power saving remote SP2) a complimented 7 bit Barker sequence
is sent every 256 preamble cycles as a 'Please Hold The Line' code. An 8th balancing bit is added after
the Barker sequence.
Radiometrix Ltd, SP2 data sheet
page 17