Rainbow Electronics ATmega128RFA1 - Manual (Page 61)

61
8266A-MCU Wireless-12/09
ATmega128RFA1
Register Name Description
IEEE_ADDR7
….
IEEE_ADDR0
PAN_ID1
PAN_ID0
SHORT_ADDR1
SHORT_ADDR0
Address filter configuration
Short address, PAN-ID and IEEE address
XAH_CTRL_0 TX_ARET control, retries value control
CSMA_SEED_0 CSMA-CA seed value
CSMA_SEED_1 CSMA-CA seed value, RX_AACK control
CSMA_BE CSMA-CA back-off exponent control
9.5 Functional Description
9.5.1 Introduction – IEEE 802.15.4-2006 Frame Format
Figure 9-14 below provides an overview of the physical layer (PHY) frame structure as
defined by IEEE 802.15.4. Figure 9-15 on page 62 shows the frame structure of the
medium access control (MAC) layer.
Figure 9-14. IEEE 802.15.4 Frame Format - PHY-Layer Frame Structure (PPDU)
9.5.1.1 PHY Protocol Layer Data Unit (PPDU)
9.5.1.1.1 Synchronization Header (SHR)
The SHR consists of a four-octet preamble field (all zero), followed by a single byte
start-of-frame delimiter (SFD) which has the predefined value 0xA7. During transmit,
the SHR is automatically generated by the radio transceiver, thus the Frame Buffer
shall contain PHR and PSDU only.
The transmission of the SHR requires 160 µs (10 symbols). As the frame buffer access
is normally faster than the over-air data rate, this allows the application software to
initiate a transmission without having transferred the full frame data already. Instead it is
possible to subsequently write the frame content.
During frame reception, the SHR is used for synchronization purposes. The matching
SFD determines the beginning of the PHR and the following PSDU payload data.
9.5.1.1.2 PHY Header (PHR)
The PHY header is a single octet following the SHR. The least significant 7 bits denote
the frame length of the following PSDU, while the most significant bit of that octet is
reserved, and shall be set to 0 for IEEE 802.15.4 compliant frames.