14.2.1.2.5 RX_ON and BUSY_RX - RX Listen and Receive State

In RX_ON state the receiver is in the RX data polling mode and the PLL frequency synthesizer is locked to its preprogrammed frequency.

The AT86RF212B receive mode is internally separated into RX_ON state and BUSY_RX state. There is no difference between these states with respect to the analog radio transceiver circuitry, which are always turned on. In both states, the receiver and the PLL frequency synthesizer are enabled.

During RX_ON state, the receiver listens for incoming frames. After detecting a valid synchronization header (SHR), the AT86RF212B automatically enters the BUSY_RX state. The reception of a valid PHY header (PHR) generates an IRQ_2 (RX_START) if enabled.

During PSDU reception, the frame data are stored continuously in the Frame Buffer until the last byte was received. The completion of the frame reception is indicated by an interrupt IRQ_3 (TRX_END) and the radio transceiver reenters the state RX_ON. At the same time the RX_CRC_VALID bits in the PHY_RSSI register (PHY_RSSI.RX_CRC_VALID) is updated with the result of the FCS check.

Received frames are passed to the frame filtering unit. If the content of the MAC addressing fields (refer to [2] IEEE 802.15.4-2006, Section 7.2.1) generates a match, IRQ_5 (AMI) interrupt is issued. The expected address values are to be stored in registers 0x20 – 0x2B (Short address, PAN-ID and IEEE address). Frame filtering is available in Basic Operating Mode and Extended Operating Mode.

Leaving state RX_ON is possible by writing a state change command to the TRX_CMD bits in the TRX_STATE register (TRX_STATE.TRX_CMD).