AT86RF212_1 Datasheet, PDF (109/171 Pages) ATMEL Corporation – Low Power 700/800/900 MHz

7.4 Frame Buffer
7.4.1 Data Management
AT86RF212
The AT86RF212 contains a 128 byte dual port SRAM. One port is connected to the SPI
interface, the other one to the internal transmitter and receiver modules. For data
communication, both ports are independent and simultaneously accessible.
The Frame Buffer utilizes the SRAM address space 0x00 to 0x7F for RX and TX
operation of the radio transceiver and can keep a single IEEE 802.15.4 RX or a single
TX frame of maximum length at a time.
Frame Buffer access modes are described in section 4.3.2. Frame Buffer access
conflicts are indicated by an underrun interrupt IRQ_6 (TRX_UR). Note that this
interrupt also occurs on the attempt to write frames longer than 127 octets to the Frame
Buffer (overflow). In this case, the content of the Frame Buffer is undefined.
Frame Buffer access is only possible if the digital voltage regulator is turned on. This is
valid in all device states except in SLEEP state. An access in P_ON state is possible
once pin 17 (CLKM) provides the 1 MHz master clock.
Data in Frame Buffer (received data or data to be transmitted) can be changed by:
• Frame Buffer or SRAM write access over SPI
• Receiving a new frame in BUSY_RX or BUSY_RX_AACK state
• A change into SLEEP state
• A RESET
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 250 kbit/s, a minimum SPI clock rate of 1 MHz 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 the command PLL_ON to register bits TRX_CMD
(register 0x02, TRX_STATE) while or immediately after receiving the frame.
Alternatively, Dynamic Frame Buffer Protection can be used to protect received frames
against overwriting, for details refer to section 9.7.
Both procedures do not protect the Frame Buffer from overwriting by the
microcontroller.
In Extended Operating Mode during TX_ARET operation, see 5.2.4, 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.
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