2 frame receive procedure, 3 configuration, Atmega128rfa1 – Rainbow Electronics ATmega128RFA1 User Manual
Page 75
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8266A-MCU Wireless-12/09
ATmega128RFA1
converter (RX ADC) and generates a digital RSSI signal. The ADC output signal is
sampled and processed further by the digital base band receiver (RX BBP).
The RX BBP performs additional signal filtering and signal synchronization. The
frequency offset of each frame is calculated by the synchronization unit and is used
during the remaining receive process to correct the offset. The receiver is designed to
handle frequency and symbol rate deviations up to ±120 ppm caused by combined
receiver and transmitter deviations. For details refer to chapter
.
Finally the signal is demodulated and the data are stored
in the Frame Buffer.
"Basic Operating Mode" on page 35
),
the reception of a
frame is indicated by a TRX24_RX_START interrupt. Accordingly its end is signalized
by a TRX24_RX_END interrupt. Based on the quality of the received signal a link
quality indicator (LQI) is calculated and appended to the frame. For details refer to.
Additional signal processing is applied to the frame data to provide further status
information like ED value (register PHY_ED_LEVEL) and FCS correctness (register
PHY_RSSI).
Beyond these features the Extended Operating Mode of the radio transceiver supports
address filtering and pending data indication. For details refer to
9.6.1.2 Frame Receive Procedure
The frame receive procedure including the radio s setup for reception and reading
PSDU data from the Frame Buffer is described in
"Frame Receive Procedure" on page
84.
9.6.1.3 Configuration
In Basic Operating Mode the receiver is enabled by writing command RX_ON to the
TRX_CMD bits of register TRX_STATE in the states TRX_OFF or PLL_ON. Similarly in
Extended Operating Mode the receiver is enabled for RX_AACK operation from the
states TRX_OFF or PLL_ON by writing the command RX_AACK_ON. There is no
additional configuration required to receive IEEE 802.15.4 compliant frames when using
the Basic Operating Mode. However, the frame reception in the Extended Operating
Mode requires further register configurations. For details refer to
.
The receiver has an outstanding sensitivity performance of -100 dBm. At certain
environmental conditions or for High Data Rate Modes (see
it may be useful to manually decrease this sensitivity. This is achieved by
adjusting the detector threshold of the synchronization header using the
RX_PDT_LEVEL bits of register RX_SYN. Received signals with a RSSI value below
the threshold do not activate the demodulation process.
Furthermore, it may be useful to protect a received frame against overwriting by
subsequent received frames.
A Dynamic Frame Buffer Protection is enabled with register bit RX_SAFE_MODE
(TRX_CTRL_2) set (refer to
"Dynamic Frame Buffer Protection" on page 91
). After a
frame has been received, the buffer is protected for new incoming frames and the
receiver remains in RX_ON or RX_AACK_ON state until the RX_SAFE_MODE bit is
cleared by the controller. The Frame Buffer content is only protected if the FCS is valid.
A Static Frame Buffer Protection is enabled with bit RX_PDT_DIS of register RX_SYN
set. The receiver remains in RX_ON or RX_AACK_ON state and no further SHR is
detected until the register bit RX_PDT_DIS is set back.