MRF24J40_08 Datasheet, PDF (96/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
3.8.1.1 Superframe Structure
The superframe structure is shown in Figure 3-4. A
superframe is bounded by the transmission of a
beacon frame and can have an active and inactive
portion. The coordinator will interact with its PAN only
during the active portion of the superframe, and during
the inactive portion of the superframe, the coordinator
can go to a low-power mode. The active portion of the
superframe is divided into 16 equally spaced slots and
is composed of three parts: a beacon, a Contention
Access Period (CAP) and an optional Contention Free
Period (CFP). The structure of the superframe depends
FIGURE 3-4:
SUPERFRAME STRUCTURE
Backoff Period (aUnitBackoffPeriod = 20 symbols)
on the values of Beacon Order (BO) and Superframe
Order (SO). The CFP, if present, follows immediately
after the CAP and extends to the end of active portion
of the superframe. Any allocated GTSs shall be located
in the CFP of the active portion of the superframe.
All the frames transmitted in the CAP, except
Acknowledgement frames and data frames that imme-
diately follow the data request command, must use
slotted CSMA-CA. Refer to Section 3.9 “Carrier
Sense Multiple Access-Collision Avoidance
(CSMA-CA) Algorithm” for more information.
Beacon
CAP End Slot = ESLOTG1 (0x13<3:0>)
GTS End Slots = ESLOTG23 (0x1E),
ESLOTG45 (0x1F), ESLOT67 (0x20)
Slot
G
012345678
GTS1
T
S
GTS3
2
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Inactive Portion
CAP
Active Portion
CFP
Inactive Portion
Superframe Duration (SD) = aBaseSuperframeDuration * 2^SO symbols
(SO – ORDER 0x10<3:0>)
SD
Beacon Interval (BI) = aBaseSuperframeDuration * 2^BO symbols
(BO – ORDER 0x10<7:4>)
BI
Beacon
DS39776B-page 94
Preliminary
© 2008 Microchip Technology Inc.