AXM0F243 datasheet(35/53 Pages) ONSEMI

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AXM0F243

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Registers

Table 47. CHANNEL FILTER AND DEMODULATOR REGISTERS

Remarks

AX5043_DECIMATION

This register programs the bandwidth of the digital channel filter.

AX5043_RXDATARATE2… AX5043_RX-

DATARATE0

These registers specify the receiver bit rate, relative to the channel filter bandwidth.

AX5043_MAXDROFFSET2…

AX5043_MAXDROFFSET0

These registers specify the maximum possible data rate offset

AX5043_MAXRFOFFSET2… AX5043_MAXR-

FOFFSET0

These registers specify the maximum possible RF frequency offset

AX5043_TIMEGAIN, AX5043_DRGAIN

These registers specify the aggressiveness of the receiver bit timing recovery. More

aggressive settings allow the receiver to synchronize with shorter preambles, at the

expense of more timing jitter and thus a higher bit error rate at a given signal−to−noise

ratio.

AX5043_MODULATION

This register selects the modulation to be used by the transmitter and the receiver,

i.e. whether ASK, FSK should be used.

AX5043_PHASEGAIN, AX5043_FREQGAINA,

AX5043_FREQGAINB, AX5043_FREQGAINC,

AX5043_FREQGAIND, AX5043_AMPLGAIN

These registers control the bandwidth of the phase, frequency offset and amplitude

tracking loops.

AX5043_AGCGAIN

This register controls the AGC (automatic gain control) loop slopes, and thus the

speed of gain adjustments. The faster the bit−rate, the faster the AGC loop should be.

AX5043_TXRATE

These registers control the bit rate of the transmitter.

AX5043_FSKDEV

These registers control the frequency deviation of the transmitter in FSK mode. The

receiver does not explicitly need to know the frequency deviation, only the channel

filter bandwidth has to be set wide enough for the complete modulation to pass.

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

AX5043_ENCODING, details and recommendations on

usage are given in the AX5043 Programming Manual.

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 microcontroller 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 AXM0F243 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 microcontroller must

periodically read the FIFO status register or the FIFO count

In interrupt mode EMPTY, NOT EMPTY, FULL, NOT

FULL and programmable level interrupts are provided.

Interrupts are acknowledged by removing the cause for the

interrupt, i.e. by emptying or filling the FIFO.

AXM0F243 Datasheet(PDF) 35 Page - ON Semiconductor

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