14.4.4.1 Data Management

Data in Frame Buffer (received data or data to be transmitted) remains valid as long as:

• No new frame or other data are written into the buffer over SPI
• No new frame is received (in any BUSY_RX state)
• No state change into SLEEP state is made
• No RESET took place

By default, there is no protection of the Frame Buffer against overwriting. Therefore, if a frame is received during Frame Buffer read access of a previously received frame, interrupt IRQ_6 (TRX_UR) is issued and the stored data might be overwritten.

Even so, the old frame data can be read, if the SPI data rate is higher than the effective over air data rate. For a data rate of 250kb/s, a minimum SPI clock rate of 1MHz is recommended. Finally, the microcontroller should check the transferred frame data integrity by an FCS check.

To protect the Frame Buffer content against being overwritten by newly incoming frames, the radio transceiver state should be changed to PLL_ON state after reception. This can be achieved by writing immediately the command PLL_ON to the TRX_CMD bits in the TRX_STATE register (TRX_STATE.TRX_CMD) after receiving the frame, indicated by IRQ_3 (TRX_END). Alternatively, Dynamic Frame Buffer Protection can be used to protect received frames against overwriting. Both procedures do not protect the Frame Buffer from overwriting by the microcontroller.

In Extended Operating Mode during TX_ARET operation the radio transceiver switches to receive state if an acknowledgement of a previously transmitted frame was requested. During this period, received frames are evaluated but not stored in the Frame Buffer. This allows the radio transceiver to wait for an acknowledgement frame and retry the frame transmission without writing the frame again.

A radio transceiver state change, except a transition to SLEEP state or a reset, does not affect the Frame Buffer content. If the radio transceiver is taken into SLEEP, the Frame Buffer is powered off and the stored data get lost.