CC2420 Datasheet, PDF (40/87 Pages) List of Unclassifed Manufacturers – 2.4 GHz IEEE 802.15.4 / ZigBee-ready RF Transceiver

SmartRF ^® CC2420
If a frame is rejected, CC2420 will only start
searching for a new frame after the
rejected frame has been completely
received (as defined by the length field) to
avoid detecting false SFDs within the
frame.
The
MDMCTRL0.PAN_COORDINATOR
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.
Acknowledge Frames
CC2420 includes hardware support for
transmitting acknowledge frames, as
specified in [1]. Figure 22 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
also ADR_DECODE and AUTOCRC are
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 18) 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.
Bytes: 4
1
1
Preamble
Sequence
Start of Frame
Delimiter
(SFD)
Frame
Length
Synchronisation Header
PHY Header
(SHR)
(PHR)
2
1
Frame
Data
Control Field Sequence
(FCF)
Number
MAC Header (MHR)
2
Frame Check
Sequence
(FCS)
MAC Footer
(MFR)
Figure 22. Acknowledge frame format [1]
Two command strobes, SACK and
SACKPEND are defined to transmit
acknowledge frames with the frame
pending field cleared or set, respectively.
The acknowledge frame is only
transmitted if the CRC is valid.
For systems using beacons, there is an
additional timing requirement that the
acknowledge frame transmission should
be started on the first backoff-slot
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 23.
If a SACK or SACKPEND command strobe
is issued while receiving an incoming
frame, the acknowledge frame is
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 23.
Using SACKPEND will set the pending data
flag for automatically transmitted
acknowledge frames using AUTOACK. The
pending flag will then be set also for future
acknowledge frames, until a SACK
command strobe is issued.
Acknowledge frames may be manually
transmitted using normal data
transmission if desired.
Chipcon AS SmartRF^® CC2420 Preliminary Datasheet (rev 1.2), 2004-06-09
Page 40 of 87