CC2420-RTR1 datasheet(36/92 Pages) TI

36 / 92 page

CC2420

SWRS041B

Page 36 of 89

Digital

IF Channel

Filtering

ADC

Digital

Data

Filtering

Frequency

Offset

Compensation

Symbol

Correlators and

Synchronisation

RSSI

Generator

I / Q Analog

IF signal

Data

Symbol

Output

RSSI

Average

Correlation

Value (may be

used for LQI)

Figure 16. Demodulator Simplified Block Diagram

16 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 17 [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].

Figure 17. Schematic view of the IEEE 802.15.4 Frame Format [1]

16.1

Synchronisation header

The

synchronisation

header

(SHR)

consists

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.

CC2420, 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 synchronisation header is always

transmitted first in all transmit modes.

The preamble sequence length can be set

by MDMCTRL0.PREAMBLE_LENGTH, while

the SFD is programmed in the SYNCWORD

gives the user some extra flexibility as

described below. Figure 18 shows how the

CC2420 synchronisation 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 SYNCWORD register so that

the

CC2420 preamble sequence is only 6

symbols long for compliance with [1]. Two

PHY

Layer

Frame

Control Field

(FCF)

Data

Sequence

Number

Bytes:

Address

Information

0 to 20

Frame payload

Frame Check

Sequence

(FCS)

MAC Header (MHR)

MAC Payload

MAC Footer

(MFR)

Frame

Length

MAC Protocol

Data Unit

(MPDU)

Start of frame

Delimiter

(SFD)

Bytes:

5 + (0 to 20) + n

Preamble

Sequence

Synchronisation Header

(SHR)

PHY Header

(PHR)

PHY Service Data Unit

(PSDU)

PHY Protocol Data Unit

(PPDU)

11 + (0 to 20) + n

MAC

Layer

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