14.5.1 Frame Receive Procedure

A frame reception comprises of two actions: The transceiver listens for, receives, and demodulates the frame to the Frame Buffer and signals the reception to the microcontroller. After or during that process, the microcontroller can read the available frame data from the Frame Buffer via the SPI interface.

While being in state RX_ON or RX_AACK_ON, the radio transceiver searches for incoming frames with the selected modulation scheme and data rate on the selected channel. Assuming the appropriate interrupts are enabled, the detection of a frame is indicated by interrupt IRQ_2 (RX_START). When the frame reception is completed, interrupt IRQ_3 (TRX_END) is issued.

Different Frame Buffer read access scenarios are recommended for:

• Non-time critical applications:
  • Read access starts after IRQ_3 (TRX_END)
• Time-critical applications:
  • Read access starts after IRQ_2 (RX_START)

For non-time-critical operations, it is recommended to wait for interrupt IRQ_3 (TRX_END) before starting a Frame Buffer read access. The figure below illustrates the frame receive procedure using IRQ_3 (TRX_END).

Critical protocol timing could require starting the Frame Buffer read access after interrupt IRQ_2 (RX_START). The first byte of the frame data can be read 32µs after the IRQ_2 (RX_START) interrupt. The microcontroller must ensure to read slower than the frame is received. Otherwise a Frame Buffer under run occurs, IRQ_6 (TRX_UR) is issued, and the frame data may be not valid. To avoid this, the Frame Buffer read access can be controlled by using a Frame Buffer Empty Indicator.