Texas Instruments 3138 155 232931 - Manual (Page 42)

CC2420
SWRS041B Page 42 of 89
AUTOACK
may be used for non-beacon
systems as long as the frame pending
field (see Figure 19) 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.
Frame
Control Field
(FCF)
Data
Sequence
Number
2 1
Frame Check
Sequence
(FCS)
2
MAC Header (MHR) MAC Footer
(MFR)
Frame
Length
Start of Frame
Delimiter
(SFD)
Bytes: 1 1
Preamble
Sequence
4
Synchronisation Header
(SHR)
PHY Header
(PHR)
Figure 23. 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 24.
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 24.
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.
PPDU Acknowledge
Non-beacon
network
t
ack
= 12 symbol periods
PPDU Acknowledge
Beacon
network
t
ack
< 32 symbol periods 12 symbol periods <=
La
st
PP
DU
sy
m
bo
l
Ba
ck
of
f s
lot
b
ou
nd
ar
y
12
symbol
periods
S
A
C
K
/
S
A
C
K
P
E
N
D
Figure 24. Acknowledge frame timing