MRF24J40_08 Datasheet, PDF (102/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
To configure the MRF24J40 for Unslotted CSMA-CA
mode, clear SLOTTED (TXMCR 0x11<5>) bit = 0.
The macMinBE and macMaxCSMABackoff values in
the MRF24J40 are set to the IEEE 802.15.4 Standard
defaults. To program their values:
• macMinBE – Program MACMINBE (TXMCR
0x11<4:3>) bits to a value between 0 and 3 (the
IEEE 802.15.4 Standard default is 3).
• macMaxCSMABackoff – Program CSMABF
(TXMCR 0x11<2:0>) bits to a value between 0
and 5 (the IEEE 802.15.4 Standard default is 4).
3.9.2 SLOTTED CSMA-CA MODE
Figure 3-7 shows the slotted CSMA-CA algorithm. This
mode is used on a beacon-enabled network where the
backoff period boundaries of every device on the network
shall be aligned with the superframe slot boundaries of
the PAN coordinator. Refer to IEEE 802.15.4-2003,
Section 7.5.1.3 “The CSMA-CA Algorithm” for more infor-
mation.
Configuring the MRF24J40 for beacon-enabled
network operation is covered in Section 3.8.1
“Beacon-Enabled Network”.
FIGURE 3-7:
SLOTTED CSMA-CA ALGORITHM
Start
NB = 0, CW = 2
Battery Life Extension
BATLIFEXT (TXMCR 0x11<6>)
macMinBE
MACMINBE (TXMCR 0x11<4:3>)
Battery Life
Y
Extension?
N
BE = macMinBE
BE = lesser(2, macMinBE)
Locate for Backoff Period Boundary
Delay for Random (2^BE – 1) Unit Backoff Periods
Perform CCA on Backoff Period Boundary
Y
Channel Idle?
N
CW = 2, NB = NB + 1, BE = min(BE+1, aMaxBE)
CW = CW – 1
N
NB > macMaxCSMABackoffs?
macMaxCSMABackoffs
CSMABF (TXMCR 0x11<2:0>)
Y
FAILURE
(Report Channel Access
Failure to Host
Microcontroller)
N
CW = 0?
Y
Transmit Pending Packet
(SUCCESS)
DS39776B-page 100
Preliminary
© 2008 Microchip Technology Inc.