Rainbow Electronics ATmega128RFA1 - Manual (Page 90)

90
8266A-MCU Wireless-12/09
ATmega128RFA1
If the radio transceiver is not in a receive or transmit state, it is recommended to disable
register bit ANT_EXT_SW_EN and to set the port pins DIG1 and DIG2 to output low
(DDG1 = 1, PORTG1 = 0, DDF2 = 1, PORTF2 = 0) in order to reduce the power
consumption or avoid leakage current of the external RF switch especially during sleep
modes.
9.8.3.3 Antenna Diversity with Extended Operation Modes
A combination of Extended Operation Mode and antenna diversity is allowed.
While the radio transceiver is in RX_AACK_ON state, it switches to an antenna with a
reliable signal. The receive antenna selection is also used for transmission of an
automatic acknowledge frame.
While the radio transceiver is in TX_ARET state, the selected antenna is automatically
changed for every frame transmission retry.
9.8.3.4 Antenna Diversity Sensitivity Control
The detection threshold of the receiver has to be adjusted due to a different receive
algorithm used by the Antenna Diversity algorithm. It is recommended to set bits
PDT_THRES of register RX_CTRL to 3.
9.8.4 RX/TX Indicator
The main features are:
• RX/TX Indicator to control an external RF Front-End;
• Application software independent RF Front-End Control;
• Provide TX Timing Information;
9.8.4.1 Overview
While IEEE 802.15.4 is a low-cost, low-power standard, solutions supporting higher
transmit output power are occasionally desirable. A differential control pin pair can
indicate that the radio transceiver is currently in transmit mode to simplify the control of
an optional external RF front-end.
The control of an external RF front-end is done via the digital control pins DIG3/DIG4.
The function of this pin pair is enabled with bit PA_EXT_EN of register TRX_CTRL_1.
Pin DIG3 is set to low level and DIG4 to high level
while the transmitter is turned off.
The two pins change the polarity when the radio transceiver starts transmitting. This
differential pin pair can be used to control PA, LNA and RF switches.
If the radio transceiver is not in a receive or transmit state, it is recommended to disable
register bit PA_EXT_EN and to set the port pins DIG3 and DIG4 to output low (DDG0 =
1, PORTG0 = 0, DDF3 = 1, PORTF3 = 0) in order to reduce the power consumption or
avoid leakage current of external RF switches and other building blocks especially
during sleep modes.
9.8.4.2 External RF-Front End Control
The setup time of the external power amplifier (PA) relative to the internal building
blocks should be adjusted when using an external RF front-end including a power
amplifier to optimize the overall power spectral density (PSD) mask.