Rainbow Electronics ATmega128RFA1 - Manual (Page 85)

85
8266A-MCU Wireless-12/09
ATmega128RFA1
command TX_START to register TRX_STATE after a Frame Buffer write access and
while the radio transceiver is in state PLL_ON or TX_ARET_ON. The TRX24_TX_END
interrupt indicates the completion of the transaction.
Figure 9-28. Transaction between radio transceiver and microcontroller during transmit
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Write frame data (Frame Buffer access)
Write TRX_CMD = TX_START, or write SLPTR
(Register access)
IRQ issued (TX_END)
Alternatively a frame transmission can be started first, followed by the Frame Buffer
write access (PSDU data) as shown in
Figure 9-29 below . This is applicable for time
critical applications.
A transmission is initiated either by writing SLPTR or by writing the TX_START
command to the TRX_CMD bits of register TRX_STATE. The radio transceiver then
starts transmitting the SHR which is internally generated.
This first phase requires 16 µs for PLL settling and 160 µs for SHR transmission. The
PHR must be available in the Frame Buffer before this time elapses. Furthermore the
Frame Buffer must be filled faster than the frame is transmitted to prevent a buffer
under-run.
Figure 9-29. Time Optimized Frame Transmit Procedure
Write frame data (Frame Buffer access)
Write TRX_CMD = TX_START, or write SLPTR
(Register access)
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IRQ issued (TX_END)
9.8 Radio Transceiver Extended Feature Set
9.8.1 Random Number Generator
The radio transceiver incorporates a 2-bit, noise observing, true random number
generator to be used to:
• Generate random seeds for CSMA-CA algorithm (see "Extended Operating Mode" on
page 43 );