CC2430 Datasheet, PDF (178/234 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
14.19 Acknowledge Frames
CC2430 includes hardware support for
transmitting acknowledge frames, as
specified in [1]. Figure 50 shows the
format of the acknowledge frame.
If MDMCTRL0L.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 ADDR_DECODE and AUTOCRC are
enabled. The sequence number is copied
from the incoming frame.
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 50: 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 may be
started on the first backoff-slot boundary
(20 symbol periods) at least 12 symbol
periods after the last symbol of the
incoming frame. When the RF register
control bit MDMCTRL1H.SLOTTED_ACK is
set to 1, the acknowledge frame is
transmitted between 12 and 30 symbol
periods after the incoming frame. The
timing is defined such that there is an
integer number of 20-symbol period
backoff-slots between the incoming packet
SFD and the transmitted acknowledge
frame SFD. This timing is also illustrated in
Figure 51.
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. The pending
data flag that is transmitted will be logically
OR’ed with the value of
FSMTC1.PENDING_OR. Thus the pending
flag can be set high using this register
control bit.
Acknowledge frames may be manually
transmitted using normal data
transmission if desired.
CC2430 PRELIMINARY Data Sheet (rev. 1.03) SWRS036A
Page 178 of 232