MRF24J40MB-I Datasheet, PDF (104/156 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
Start
NB = 0, CW = 2
NB = 0, CW = 2
Battery Life Extension
BATBLIaFtEteXryT L(TifXeMECxRten0sx1io1n<6>)
BATLIFEXT (TXMCR 0x11<6>)
macMinBE
MACMINBEm(aTcXMMiCnBRE0x11<4:3>)
MACMINBE (TXMCR 0x11<4:3>)
Battery Life
EBxatetenrsyioLnif?e
Y
Y
Extension?
N
N
BE = macMinBE
BE = macMinBE
Locate for Backoff Period Boundary
Locate for Backoff Period Boundary
BE = lesser(2, macMinBE)
BE = lesser(2, macMinBE)
Delay for Random (2^BE – 1) Unit Backoff Periods
Delay for Random (2^BE – 1) Unit Backoff Periods
Perform CCA on Backoff Period Boundary
Perform CCA on Backoff Period Boundary
Y
Channel Idle?
Y
Channel Idle?
N
N
CW = 2, NB = NB + 1, BE = min(BE+1, aMaxBE)
CW = 2, NB = NB + 1, BE = min(BE+1, aMaxBE)
CW = CW – 1
CW = CW – 1
N
N
macMaxCSMABackoffs
CSMmaAcBMFa(xTCXSMMCABRa0cxk1o1f<f2s:0>)
CSMABF (TXMCR 0x11<2:0>)
NB > macMaxCSMABackoffs?
NB > macMaxCSMABackoffs?
Y
Y
(R(RepeMFopMraiFoctFirairlCctuoAFirlChrcuoIAeLaohrcIeUnntLaoontUnnRtroeHontRErlleHoolEAellsolrAcet)scrct)ecsesss
CCCCAAFAFAILIL(T(TXXSSTTAATT00x2x24<4<55>>) ₎
N
CW = 0?
N
CW = 0?
Y
Y
SUCCESS
(TransmiSt UPCenCdEinSgSPacket)
(T_Tra_Xn_Nsm_STit _AP_Ten₍d_Tin_Xg_SP_Ta_Ack_Tet)
TXNS0xT2A4T<(0T>X)STAT
0x24<0>)
DS39776C-page 104
Preliminary
© 2010 Microchip Technology Inc.