CC2430 Datasheet, PDF (161/212 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

I / Q Analog
IF signal
ADC
Radio : Frame Format
Digital
IF Channel
Filtering
Frequency
Offset
Compensation
Digital
Data
Filtering
CC2430
Symbol
Correlators and
Synchronisation
Data
Symbol
Output
RSSI
Generator
RSSI
Figure 38: Demodulator Simplified Block Diagram
Average
Correlation
Value (may be
used for LQI)
14.12 Frame Format
CC2430 has hardware support for parts of the
IEEE 802.15.4 frame format. This section
gives a brief summary to the IEEE 802.15.4
frame format, and describes how CC2430 is
set up to comply with this.
Figure 39 [1] 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 [1].
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 39: Schematic view of the IEEE 802.15.4 Frame Format [1]
14.13 Synchronization header
The synchronization header (SHR) consists of
the preamble sequence followed by the start of
frame delimiter (SFD). In [1], the preamble
sequence is defined to be four bytes of 0x00.
The SFD is one byte, set to 0xA7.
In CC2430, the preamble length and SFD is
configurable. The default values are compliant
with [1]. Changing these values will make the
system non-compliant to IEEE 802.15.4.
A synchronization header is always
transmitted first in all transmit modes.
The preamble sequence length can be set with
RF
register
bit
MDMCTRL0L.PREAMBLE_LENGTH, while the
SFD is programmed in the
SYNCWORDH:SYNCWORDL
registers.
SYNCWORDH:SYNCWORDL is two bytes long,
which gives the user some extra flexibility as
described below. Figure 40 shows how the
CC2430 synchronization header relates to the
IEEE 802.15.4 specification.
The programmable preamble length only
applies to transmission, it does not affect
receive mode. The preamble length should not
be set shorter than the default value. Note that
2 of the 8 zero-symbols in the preamble
sequence required by [1] are included in the
SYNCWORDH:SYNCWORDL registers so that the
CC2430 preamble sequence is only 6 symbols
long for compliance with [1]. Two additional
zero symbols in SYNCWORDH:SYNCWORDL
make CC2430 compliant with [1].
In reception, CC2430 synchronizes to received
zero-symbols and searches for the SFD
sequence
defined
by
the
SYNCWORDH:SYNCWORDL registers. The least
significant
symbols
in
SYNCWORDH:SYNCWORDL set to 0xF will be
ignored, while symbols different from 0xF will
be required for synchronization. The default
setting of 0xA70F thereby requires one
additional zero-symbol for synchronization.
This will reduce the number of false frames
detected due to noise.
CC2430 Data Sheet (rev. 2.1) SWRS036F
Page 161 of 211