AT86RF230_09 ATMEL [ATMEL Corporation], AT86RF230_09 Datasheet - Page 35

• Manufacturer Part Number: AT86RF230_09
• Description: Low Power 2.4 GHz Transceiver for ZigBee, IEEE 802.15.4, 6LoWPAN, RF4CE and ISM
• Manufacturer: ATMEL [ATMEL Corporation]

AT86RF230
7.2.3.2 TX_ARET_ON – Transmit with Automatic CSMA-CA Retry
The implemented TX_ARET algorithm is shown in Figure 7-8.
The TX_ARET transaction is started by either a rising edge on SLP_TR pin or by writing
a TX_START command to register 0x02 (TRX_STATE). The radio transceiver sets the
TRAC_STATUS bits to INVALID and executes the CSMA-CA algorithm as defined by
IEEE 802.15.4-2003 section 7.5.1.4. If a clear channel is detected during CSMA-CA
execution, the radio transceiver proceeds to transmit the frame.
During frame transmission the AT86RF230 parses the frame control field of the
downloaded frame to check if an ACK reply is expected. If an ACK is expected, the
radio transceiver switches into receive mode to wait for valid ACK reply. An ACK is
considered as valid if its FCS is correct, and if the sequence number of the ACK
matches the sequence number of the previously transmitted frame.
If no valid ACK is received or a timeout (after 864 μs) occurred, the radio transceiver
retries the entire transaction, including CSMA-CA execution. This repeats until the
frame has been acknowledged or the maximum number of retransmissions (as set by
the register bits MAX_FRAME_RETRIES in register 0x2C) has been reached. In this
case, the TRX_END interrupt is issued and the value of TRAC_STATUS is set to
NO_ACK.
If a valid ACK is found, the TRX_END interrupt is issued. The Frame Pending subfield
of the ACK frame is parsed and the register bits TRAC_STATUS are updated. If the
frame pending subfield of the ACK frame is set, TRAC_STATUS is updated with
SUCCESS_DATA_PENDING, otherwise TRAC_STATUS is updated with SUCCESS.
While in receive mode for ACK reception, incoming data do not overwrite the Frame
Buffer content. Transmit data in the Frame Buffer are not changed during the TX_ARET
transaction.
If no ACK is expected, the radio transceiver issues a TRX_END interrupt after the frame
transmission has been completed. The value of register bits TRAC_STATUS (register
0x02) is set to SUCCESS.
If the CSMA-CA did not detect a clear channel, the channel access is retried as often as
specified by the register bits MAX_CSMA_RETRIES (register 0x2C). In case that
CSMA-CA does not detect a clear channel after MAX_CSMA_RETRIES, the
transaction is aborted and the TRX_END interrupt is issued. The TRAC_STATUS
register bits are updated with CHANNEL_ACCESS_FAILURE.
Note that it is recommended to download the transmit data before starting a TX_ARET
transaction.
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5131E-MCU Wireless-02/09