14.2.2.4.2 Timing
A timing example of a TX_ARET transaction is shown in figure below. In the example shown, a data frame with an acknowledgment request is to be transmitted. The frame transmission is started by sending a pulse on pin 11 (SLP_TR). By setting the MIN_BE bits in the CSMA_BE register (CSMA_BE.MIN_BE) to zero, the initial CSMA-CA backoff period is configured to zero length. Thus, the CSMA-CA duration time tCSMA-CA consists only of eight symbols of CCA measurement period. If CCA returns IDLE (assumed here), the frame is transmitted.
Upon frame transmission AT86RF212B switches to the receive mode and expects an acknowledgement response. This is indicated by the TRAC_STATUS bits in the TRX_STATE register (TRX_STATE.TRAC_STATUS) set to SUCCESS_WAIT_FOR_ACK. After a period of aTurnaroundTime + aUnitBackoff, the transmission of the ACK frame must be started. During the entire transaction, including frame transmit, wait for ACK, and ACK receive, the radio transceiver TRX_STATUS bits in the TRX_STATUS register (TRX_STATUS.TRX_STATUS) are set to BUSY_TX_ARET state.
A successful reception of the acknowledgment frame is indicated by triggering of IRQ_3 (TRX_END). The TRX_STATUS.TRX_STATUS bits changes back to TX_ARET_ON state. When the frame pending subfield of the received ACK frame is set to one (more data is to follow) the TRAC_STATUS bits in the TRX_STATE register (TRX_STATE.TRAC_STATUS) are set either to SUCCESS_DATA_PENDING status instead of SUCCESS status.
