EM2420 ETC [List of Unclassifed Manufacturers], EM2420 Datasheet - Page 34

• Manufacturer Part Number: EM2420
• Description: 2.4 GHz IEEE 802.15.4 / ZigBee RF Transceiver
• Manufacturer: ETC [List of Unclassifed Manufacturers]

The EM2420 has hardware support for
parts of the IEEE 802.15.4 frame format.
This section gives a brief summary to the
IEEE
describes how the EM2420 is set up to
comply with this.
Figure 15. Schematic view of the IEEE 802.15.4 Frame Format [1]
Synchronization header
The
consists
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.
In the EM2420, the preamble length and
SFD is configurable. The default values
are compliant with [1]. Changing these
values will make the system non-802.15.4-
compliant, which could be desirable in
some cases.
A
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
register. SYNCWORD is 2 bytes long, which
gives the user some extra flexibility as
described below. Figure 16 shows how the
EM2420 synchronisation header relates to
the IEEE 802.15.4 specification.
The programmable preamble length only
applies to transmission, it does not affect
Ember Part Number: 120-0049-000C
Layer
Layer
MAC
PHY
synchronisation
Bytes:
synchronisation
802.15.4
Sequence
Preamble
Synchronisation Header
of
4
the
(SHR)
frame
Start of Frame
preamble
header
Delimiter
(SFD)
1
header
format,
PHY Header
Length
is
Frame
(PHR)
sequence
1
always
(SHR)
Bytes:
and
EM2420 Datasheet
Control Field
Frame
(FCF)
2
PHY Protocol Data Unit
11 + (4 to 20) + n
MAC Header (MHR)
(PPDU)
Sequence
Number
Figure 15 [1] shows a schematic view of
the IEEE 802.15.4 frame format. Similar
figures describing specific frame formats
(data
acknowledgment
command frames) are included in [1].
receive
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 EM2420 preamble sequence is only 6
symbols long for compliance with [1]. Two
additional zero symbols in SYNCWORD
make the EM2420 compliant with [1].
In reception, the EM2420 synchronizes to
received zero-symbols and searches for
the
SYNCWORD register. The least significant
symbols in SYNCWORD set to 0xF will be
ignored, while symbols different from 0xF
will be required for synchronisation. The
default setting of 0xA70F thereby requires
one
synchronisation. This will reduce the
number of false frames detected due to
noise.
In receive mode, the EM2420 uses the
preamble
synchronisation
adjustments. The SFD is used for byte
synchronisation, and is not part of the data
stored in the receive buffer (RXFIFO).
Data
1
SFD
Information
additional
Address
mode.
0 to 20
PHY Service Data Unit
frames,
5 + (0 to 20) + n
MAC Protocol
sequence
Data Unit
sequence
(MPDU)
(PSDU)
and
The
frames
Frame payload
MAC Payload
beacon
zero-symbol
EM2420
frequency
preamble
defined
n
for
and
Page 34 of 89
by
frames,
symbol
Frame Check
length
MAC Footer
offset
MAC
Sequence
(FCS)
(MFR)
the
for
2