AX5243 datasheet(33/65 Pages) ONSEMI

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Circuit Description

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AX5243

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:



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.



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 (also know as whitening). 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.

The encoder is programmed using the register

ENCODING, details and recommendations

on usage are given in the AX5243 Programming Manual.

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 two different modes:



Packet modes



Raw modes

The micro-controller communicates with the framing unit through a 256 byte FIFO. Data

in the FIFO is organized in Chunks. The chunk header encodes the length and what data

is contained in the payload. Chunks may contain packet data, but also RSSI, Frequency

Offset, Timestamps, etc.

The AX5243 contains one FIFO. Its direction is switched depending on whether transmit

or receive mode is selected.

The FIFO can be operated in polled or interrupt driven modes. In polled mode, the micro-

controller must periodically read the FIFO status register or the FIFO count register to

determine whether the FIFO needs servicing.

AX5243 датащи(PDF) 33 Page - ON Semiconductor

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