CC2420 Chipcon AS, CC2420 Datasheet - Page 37

• Manufacturer Part Number: CC2420
• Description: 2.4 GHz RF Transceiver for IEEE 802.15.4 and ZigBee
• Manufacturer: Chipcon AS

frames. This option is included for future
expansions
standard.
If a frame is rejected,
searching for a new frame after the
rejected frame has been completely
received (as defined by the length field) to
Acknowledge Frames
CC2420
transmitting
specified in [1]. Figure 21 shows the
format of the acknowledge frame.
If MDMCTRL0.AUTOACK is enabled, an
acknowledge frame is transmitted for all
incoming frames accepted by the address
recognition with the acknowledge request
flag set and a valid CRC. AUTOACK
therefore does not make sense unless
Two
SACKPEND
acknowledge
pending field cleared or set, respectively.
The
transmitted if the CRC is valid.
For systems using beacons, there is an
additional timing requirement that the
acknowledge frame transmission should
be
boundary (20 symbol periods) at least 12
symbol periods after the last symbol of the
incoming frame. This timing must be
controlled by the microcontroller by issuing
the SACK and SACKPEND command strobe
12 symbol periods before the following
backoff-slot boundary, as illustrated in
Figure 22.
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
Bytes:
started
command
acknowledge
Sequence
Preamble
Synchronisation Header
includes hardware support for
4
are
acknowledge
on
of
frames
(SHR)
the
the
defined
strobes,
CC2420
frame
Start of Frame
with
first
IEEE
Figure 21. Acknowledge frame format [1]
Delimiter
(SFD)
will only start
to
frames,
1
SACK
backoff-slot
the
is
802.15.4
transmit
frame
only
PHY Header
and
as
Length
Frame
(PHR)
1
SmartRF
avoid detecting false SFDs within the
frame.
The
control bit must be correctly set, since
parts of the address recognition procedure
requires knowledge about whether the
current device is a PAN coordinator or not.
also ADR_DECODE and AUTOCRC
enabled. The sequence number is copied
from the incoming frame.
AUTOACK may be used for non-beacon
systems as long as the frame pending
field (see Figure 17) is cleared. The
acknowledge frame is then transmitted 12
symbol periods after the last symbol of the
incoming frame. This is as specified by [1]
for non-beacon networks.
If a SACK or SACKPEND command strobe
is issued while receiving an incoming
frame,
transmitted 12 symbol periods after the
last symbol of the incoming frame. This
should be used to transmit acknowledge
frames in non-beacon networks. This
timing is also illustrated in Figure 22.
Using SACKPEND will set the pending data
flag
acknowledge frames using AUTOACK. The
pending flag will then be set also for future
acknowledge
command strobe is issued.
Acknowledge frames may be manually
transmitted
transmission if desired.
Control Field
MAC Header (MHR)
Frame
(FCF)
for
2
the
MDMCTRL0.PAN_COORDINATOR
automatically
acknowledge
frames,
using
Sequence
®
Number
Data
1
CC2420
until
normal
transmitted
Page 37 of 85
Frame Check
frame
MAC Footer
Sequence
a
(MFR)
(FCS)
2
SACK
data
are
is