CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
14 Exceptions
Exceptions in CC2520 are used to indicate that different events have occurred. Exceptions are used both for
error conditions such as incorrect use of the SPI and for events that are perfectly normal and expected such
as transmission of a start of frame delimiter (SFD). Exception flags are stored in status registers and can be
read over the SPI or observed on GPIO. To clear an exception flag, the user must write ‘0’ to the correct bit
in the status register. If the user tries to clear an exception flag in the exact same clock period as the same
exception occurs, the flag will not be cleared.
exceptions are numbered. The number correspond to the bits in the EXCFLAGn registers, and must be
used when binding exceptions to instructions.
Table 14: Exceptions summary
Mnemonic
RF_IDLE
Num
(hex)
0x00
Description
The main radio FSM enters its idle state from any other state. This
exception is not generated when the FSM enters the idle state because of
a device reset.
TX frame successfully transmitted, which means that TX FIFO is empty
and no underflow occurred. Exception is not generated when TX is aborted
with SRFOFF, SRXON or STXON.
ACK frame successfully transmitted. Exception is not generated when the
acknowledge transmission is aborted with SRFOFF, SRXON or STXON.
Underflow has occurred in the TX FIFO. TX is aborted and the TX FIFO
must be flushed.
An attempt was made to write to TX FIFO while it is full. The instruction is
aborted.
An attempt has been made to read the RX FIFO without any bytes
available to read. Instruction is aborted.
Note that the RX_UNDERFLOW exception should only be used for
debugging software, and should not be trusted in a RX FIFO readout
routine. In some scenarios the RX_UNDERFLOW exception will not be
issued when a reading starts even when the RX_FIFO is empty.
An attempt has been made by RF_core to write to RX FIFO while the RX
FIFO is full. The byte that was attempted written to the RX FIFO is lost.
Reception of data is aborted and the FSM enters the rx_overflow state.
Recommended action is to issue a SFLUSHRX command strobe to empty
the RX FIFO and restart RX.
RX enable register has changed value to all zeros.
A complete frame has been received. I.E the number of bytes set by the
length field is received.
When frame filtering is enabled, this exception is generated when a frame
is accepted (happens immediately after receiving the fields required to
determine the outcome).
When source address matching is enabled, this exception is generated
upon completion of source address matching. The exception is generated
regardless of the result.
If a source match is found, this exception is generated immediately before
SRC_MATCH_DONE.
The RX FIFO is filled up with bytes that have passed address filtering to
the FIFOP threshold value defined in register, or at least one complete
frame has been written to the RX FIFO. High when FFCTRL is in the
rx_overflow state.
Start of frame delimiter received when in RX or start of frame delimiter
transmitted when in TX.
Low priority DPU operation completed. Will not be issued if operation fails
or is aborted.
TX_FRM_DONE
0x01
TX_ACK_DONE
TX_UNDERFLOW
TX_OVERFLOW
RX_UNDERFLOW
0x02
0x03
0x04
0x05
RX_OVERFLOW
0x06
RXENABLE_ZERO
RX_FRM_DONE
RX_FRM_ACCEPTED
0x07
0x08
0x09
SRC_MATCH_DONE
0x0A
SRC_MATCH_FOUND
FIFOP
0x0B
0x0C
SFD
DPU_DONE_L
0x0D
0x0E
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