MRF24J40-ISLASHT datasheet(98/156 Pages) MICROCHIP

98 / 156 page

MRF24J40

DS39776C-page 98

Preliminary

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

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.

FIGURE 3-4:

SUPERFRAME STRUCTURE

GTS1

GTS3

Inactive Portion

Active Portion

CAP

CFP

Slot

Backoff Period (aUnitBackoffPeriod = 20 symbols)

Inactive Portion

Beacon

GTS End Slots = ESLOTG23 (0x1E),

ESLOTG45 (0x1F), ESLOT67 (0x20)

Beacon

CAP End Slot = ESLOTG1 (0x13<3:0>)

456789 10 11 12 13 14 15

Superframe Duration (SD) = aBaseSuperframeDuration * 2SO symbols

(SO – ORDER 0x10<3:0>)

Beacon Interval (BI) = aBaseSuperframeDuration * 2BO symbols

(BO – ORDER 0x10<7:4>)

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