CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
19.4 TX Flow Diagram
No CSMA-CA
Unslotted CSMA-CA
Slotted CSMA-CA
Data buffering
SSAMPLECCA
Write a frame to the TX
buffer using:
- TXBUF
- TXBUFCP
- Memory access
- A combination of
these methods
This can be done
before, after or in
parallel with the TX
strobe.
Yes
(SAMPLED_CCA = 1)
Success?
STXON
STXONCCA
No
(SAMPLED_CCA = 0)
Yes
(SAMPLED_CCA = 1)
TX started?
No
(SAMPLED_CCA = 0)
TX buffer overfilled
TX is aborted by
SRXON,
STXON or SRFOFF
TX completes?
No
Why?
Yes
TX_FRM_DONE
TX_UNDERFLOW
TX_OVERFLOW
Frame transmitted successfully
Error condition
Incomplete or no frame transmission
TIME
Error condition
(left side of the flow
diagram should be
ignored since the TX
buffer is corrupted)
Between two transmissions there can be multiple other activities such as frame reception, RX FIFO access and acknowledgment transmission (using SACK, SACKPEND or
AUTOACK), or idle periods (random backoffs). This will have no side effects on the state of the TX buffer.
The placement of the SFLUSHTX strobe in the diagram shows the latest point in time where this strobe can be executed. If fewer special cases is desired, it is always possible to
use the SFLUSHTX strobe and then load or reload TXBUF with the next frame to be transmitted.
Next time...
To retransmit or
transmit a
different frame...
To (re)transmit
what is
currently in
the TX buffer...
Next time...
To retransmit or
transmit a
different frame...
To retransmit the
current frame...
To transmit a
different frame...
To transmit a
different frame...
Restart from the
top of the diagram
Do not write
anything to the TX
buffer
Restart from the
top of the diagram
Write the new
frame to the TX
buffer
(before, after or in
parallel with the
TX strobe)
SFLUSHTX
Restart from the
top of the diagram
If anything is
written to the TX
buffer, it will be
appended to the
current data.
SFLUSHTX
SFLUSHTX
Restart from the
top of the diagram
Write the next
frame to the TX
buffer
(before, after or in
parallel with the
TX strobe)
Restart from the
top of the diagram
Write the new
frame to the TX
buffer
(before, after or in
parallel with the
TX strobe)
Restart from the
top of the diagram
Write the next
frame to the TX
buffer
(before, after or in
parallel with the
TX strobe)
Figure 17: TX flow
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