CC2520_11 Datasheet, PDF (81/133 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
20.3.5 Acknowledgement Transmission
CC2520 includes hardware support for acknowledgment transmission after successful frame reception (i.e.
T
T
the FCS of the received frame must be correct). Figure 26 shows the format of the acknowledgment frame
Bytes: 4
1
1
Preamble
Sequence
Start of Frame
Delimiter
(SFD)
Frame
Length
Synchronisation Header
PHY Header
(SHR)
(PHR)
2
1
Frame
Data
Control Field Sequence
(FCF)
Number
MAC Header (MHR)
Figure 26. Acknowledge frame format
2
Frame Check
Sequence
(FCS)
MAC Footer
(MFR)
There are three variable fields in the generated acknowledgment frame:
• The pending bit, which may be controlled with command strobes and the AUTOPEND feature
• The data sequence number (DSN), which is taken automatically from the last received frame
• The FCS, which is given implicitly.
There are three different sources for setting the pending bit in an ACK frame (i.e. the SACKPEND strobe,
the PENDING_OR register bit and the AUTOPEND feature). The pending bit is set if one or more of these
sources are set.
Transmission Timing
Acknowledgment frames can only be transmitted immediately after frame reception. The transmission timing
is controlled by the FSMCTRL.SLOTTED_ACK bit:
Figure 27: Acknowledgement timing
802.15.4 requires unslotted mode in non-beacon enabled PANs, and slotted mode for beacon-enabled
PANs.
Manual Control
The SACK, SACKPEND and SNACK command strobes can only be issued during frame reception. If the
strobes are issued at any other time, they will have no effect but generating a USAGE_ERROR exception:
Figure 28: Command strobe timing
The command strobes may be issued several times during reception, however, only the last strobe will have
an effect:
• No strobe / SNACK / incorrect FCS: No acknowledgment transmission
• SACK: Acknowledgment transmission with the frame pending bit cleared
• SACKPEND: Acknowledgment transmission with the frame pending bit set
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