14.2.2.3.5 RX_AACK Slotted Operation – Slotted Acknowledgement
In networks using slotted operation the start of the acknowledgment frame, and thus the exact timing, must be provided by the microcontroller. Exact timing requirements for the transmission of acknowledgments in beacon-enabled networks are explained in IEEE 802.15.4-2006, Section 7.5.6.4.2. In conjunction with the microcontroller the AT86RF212B supports slotted acknowledgement operation. This mode is invoked by setting the SLOTTED_OPERATION bit in the XAH_CTRL_0 register (XAH_CTRL_0.SLOTTED_OPERATION) to one.
If an acknowledgment (ACK) frame is to be transmitted in RX_AACK mode, the radio transceiver expects a rising edge on pin 11 (SLP_TR) to actually start the transmission. During this waiting period, the transceiver reports SUCCESS_WAIT_FOR_ACK through the TRAC_STATUS bits in the XAH_CTRL_0 register (XAH_CTRL_0.TRAC_STATUS), see Figure 14-27. The minimum delay between the occurrence of interrupt IRQ_3 (TRX_END) and pin start of the ACK frame in slotted operation is three symbol periods.
The figure below illustrates the timing of an RX_AACK transaction in slotted operation. The acknowledgement frame is ready to transmit three symbol times after the reception of the last symbol of a data or MAC command frame indicated by IRQ_3 (TRX_END). The transmission of the acknowledgement frame is initiated by the microcontroller with the rising edge of pin 11 (SLP_TR) and starts tTR10 = 1symbol period later. The interrupt latency tIRQ is specified in the Digital Interface Timing Characteristics section.
