CC2420 Datasheet, PDF (34/87 Pages) List of Unclassifed Manufacturers – 2.4 GHz IEEE 802.15.4 / ZigBee-ready RF Transceiver

SmartRF ^® CC2420
continuous start of frame delimiter (SFD)
search.
When a SFD is detected, data is written to
the RXFIFO and may be read out by the
microcontroller at a lower bit rate than the
250 kbps generated by the receiver.
The CC2420 demodulator also handles
symbol rate errors in excess of 120 ppm
without performance degradation.
Resynchronisation
is
performed
continuously to adjust for error in the
incoming symbol rate.
The MDMCTRL1.CORR_THR control bits
should be written to 20 to set the threshold
for detecting IEEE 802.15.4 start of frame
delimiters.
I / Q Analog
IF signal
ADC
Digital
IF Channel
Filtering
Frequency
Offset
Compensation
Digital
Data
Filtering
Symbol
Correlators and
Synchronisation
Data
Symbol
Output
RSSI
Generator
RSSI
Figure 15. Demodulator Simplified Block Diagram
Average
Correlation
Value (may be
used for LQI)
Frame Format
CC2420 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
CC2420 is set up to comply with this.
Figure 16 [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 16. Schematic view of the IEEE 802.15.4 Frame Format [1]
Synchronisation header
The synchronisation header (SHR)
consists of the preamble sequence
followed by the start of frame delimiter
(SFD). In [1], the preamble sequence is
defined to be 4 bytes of 0x00. The SFD is
one byte, set to 0xA7.
Chipcon AS SmartRF^® CC2420 Preliminary Datasheet (rev 1.2), 2004-06-09
Page 34 of 87