CC2420-RTR1 datasheet(42/92 Pages) TI

42 / 92 page

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

Frame Check

Sequence

(FCS)

MAC Header (MHR)

MAC Footer

(MFR)

Frame

Length

Start of Frame

Delimiter

(SFD)

Bytes:

Preamble

Sequence

Synchronisation Header

(SHR)

PHY Header

(PHR)

Figure 23. Acknowledge frame format [1]

Two

command

strobes,

SACK

and

SACKPEND

are

defined

transmit

acknowledge frames with the frame

pending field cleared or set, respectively.

The

acknowledge

frame

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

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

SACK

command strobe is issued.

Acknowledge frames may be manually

transmitted

using

normal

data

transmission if desired.

PPDU

Acknowledge

Non-beacon

network

ack

= 12 symbol periods

PPDU

Acknowledge

Beacon

network

ack

< 32 symbol periods

12 symbol periods <=

f s

lot

symbol

periods

Figure 24. Acknowledge frame timing

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