CC2520_11 Datasheet, PDF (65/133 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
18 IEEE 802.15.4-2006 Frame Format
This section gives a brief summary of the IEEE 802.15.4 frame format [2]. CC2520 has built in support for
processing of parts of the frame. This is described in the following sections.
Figure 18 shows a schematic view of the IEEE 802.15.4 frame format. Similar figures describing specific
frame formats (data frames, beacon frames, acknowledgment frames and MAC command frames) are
included in the standard document [2].
MAC
Layer
Bytes: 2
1
0 to 20
Frame
Control Field
(FCF)
Data
Sequence
Number
Address
Information
MAC Header (MHR)
n
Frame payload
MAC Payload
Bytes: 4
1
1
PHY
Layer
Preamble
Sequence
Start of frame
Delimiter
(SFD)
Frame
Length
Synchronisation Header
PHY Header
(SHR)
(PHR)
5 + (0 to 20) + n
MAC Protocol
Data Unit
(MPDU)
PHY Service Data Unit
(PSDU)
11 + (0 to 20) + n
PHY Protocol Data Unit
(PPDU)
2
Frame Check
Sequence
(FCS)
MAC Footer
(MFR)
Figure 14: Schematic view of the IEEE 802.15.4 Frame Format [1]
18.1 PHY Layer
Synchronization Header
The synchronization header (SHR) consists of the preamble sequence followed by the start of frame
delimiter (SFD). In the IEEE 802.15.4 specification [2], the preamble sequence is defined to be 4 bytes of
0x00. The SFD is one byte with value 0xA7.
PHY Header
The PHY header consists only of the frame length field. The frame length field defines the number of bytes
in the MPDU. Note that the value of the length field does not include the length field itself. It does however
include the FCS (Frame Check Sequence), even if this is inserted automatically by CC2520 hardware.
T
T
The frame length field is 7 bits long and has a maximum value of 127. The most significant bit in the length
field is reserved, and should always be set to zero.
PHY Service Data Unit
The PHY Service Data Unit contains the MAC Protocol Data Unit (MPDU). It is the MAC layer’s
responsibility to generate/interpret the MPDU, and CC2520 has built in support for processing of some of
the MPDU subfields.
18.2 MAC Layer
The FCF, data sequence number and address information follows the length field as shown in Figure 14.
Together with the MAC data payload and Frame Check Sequence, they form the MPDU. The format of the
FCF is shown in Figure 15. For full details, please refer to the IEEE 802.15.4 specification [2].
Bits: 0-2
Frame
Type
3
Security
Enabled
4
Frame
Pending
5
Acknowledge
request
6
Intra
PAN
7-9
Reserved
10-11
Destination
addressing
mode
12-13
Reserved
Figure 15: Format of the Frame Control Field (FCF)
14-15
Source
addressing
mode
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