ax5042-1 AXSEM, ax5042-1 Datasheet - Page 25

• Manufacturer Part Number: ax5042-1
• Description: Rf Transceiver
• Manufacturer: AXSEM

5.10. Encoder
The encoder is located between the Framing Unit, the Demodulator and the Modulator. It
can optionally transform the bit-stream in the following ways:
The encoder is programmed using the register ENCODING, details and recommendations on
usage are given in the
5.11. Framing and FIFO
Most radio systems today group data into packets. The framing unit is responsible for
converting these packets into a bit-stream suitable for the modulator, and to extract packets
from the continuous bit-stream arriving from the demodulator.
The Framing unit supports three different modes:
The micro-controller communicates with the framing unit through a 3 level × 10 bit FIFO. The
FIFO decouples micro-controller timing from the radio (modulator and demodulator) timing.
The bottom 8 bit of the FIFO contain transmit or receive data. The top 2 bit are used to
convey meta information in HDLC and 802.15.4 modes. They are unused in Raw mode. The
meta information consists of packet begin / end information and the result of CRC checks.
The
receive mode is selected.
Version 2.2
•
•
•
•
•
•
•
AX5042
It can invert the bit stream.
It can perform differential encoding. This means that a zero is transmitted as no
change in the level, and a one is transmitted as a change in the level. Differential
encoding is useful for PSK, because PSK transmissions can be received either as
transmitted or inverted, due to the uncertainty of the initial phase. Differential
encoding / decoding removes this uncertainty.
It can perform Manchester encoding. Manchester encoding ensures that the
modulation has no DC content and enough transitions (changes from 0 to 1 and from
1 to 0) for the demodulator bit timing recovery to function correctly, but does so at a
doubling of the data rate.
It can perform Spectral Shaping. Spectral Shaping removes DC content of the bit
stream, ensures transitions for the demodulator bit timing recovery, and makes sure
that the transmitted spectrum does not have discrete lines even if the transmitted
data is cyclic. It does so without adding additional bits, i.e. without changing the
data rate. Spectral Shaping uses a self synchronizing feedback shift register.
HDLC
Raw
802.15.4 compliant
contains one FIFO. Its direction is switched depending on whether transmit or
AX5042
Programming Manual.
Circuit Description
Datasheet AX5042
25