MRF24J40_08 Datasheet, PDF (126/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
To transmit a secured frame, perform the following steps:
1. The host processor loads one of the four TX
FIFOs with an IEEE 802.15.4 compliant frame to
be encrypted using the format shown in
Figure 3-21.
FIGURE 3-21:
SECURITY TX FIFO FORMAT
TX FIFO
1
1
Header Frame
Length Length
(m) (m + n)
m
HHeeaaddeerr
2
1
4 – 20
MAC Sublayer
Frame Sequence
Encryption (Transmit) Control ^Number
Addressing
Fields
MHR
4
1
Frame
Counter
Key
Sequence
Counter
n
Data Payload
n–5
Encrypted Payload
MSDU
octets
4/8/16
2
Integrity
Code
FCS
MFR
octets
2. Program the corresponding TX FIFO 128-bit
security key into the Security Key FIFO memory
address, as shown in Table 3-23.
3. Select the security suite for the corresponding
TX FIFO and program the security select bits as
shown in Table 3-23. The security suite
selection values are shown in Table 3-24.
TABLE 3-24: SECURITY SUITE
SELECTION VALUE
Mode
Security Suite Select Bits
(see Table 3-23)
None
000
AES-CTR
001
AES-CCM-128
010
AES-CCM-64
011
AES-CCM-32
100
AES-CBC-MAC-128
101
AES-CBC-MAC-64
110
AES-CBC-MAC-32
111
4. Encrypt and transmit the packet by setting the
Security Enable (TXxSECEN) = 1 and Trigger
(TXxTRIG) bits = 1 for the respective TX FIFO,
as shown in Table 3-23.
5. Depending on which TX FIFO the secure packet
was transmit from, the status of the transmission
is read:
Fields appended
by TXMAC
TX Normal FIFO – A TXNIF (INTSTAT 0x31<0>) inter-
rupt will be issued. The TXNSTAT (TXSTAT 0x24<0>)
bit indicates the status of the transmission:
TXNSTAT = 0: Transmission was successful
TXNSTAT = 1: Transmission failed, retry count
exceeded
The number of retries of the most recent transmission
is contained in the TXNRETRY (TXSTAT 0x24<7:6>)
bits. The CCAFAIL (TXSTAT 0x24<5>) bit = 1 indicates
if the failed transmission was due to the channel busy
(CSMA-CA timed out).
TX GTSx FIFO – A TXG1IF (INTSTAT 0x31<1>) or
TXG2IF (INTSTAT 0x31<2>) interrupt will be issued.
The TXG1STAT (TXSTAT 0x24<1>) or TXG2STAT
(TXSTAT 0x24<2>) bit indicates the status of the
transmission:
TXGxSTAT = 1: Transmission was successful
TXGxSTAT = 0: Transmission failed, retry count
exceeded
The number of retries of the most recent transmission
is contained in the TXG1RETRY (TXG1CON
0x1C<7:6>) or TXG2RETRY (TXG2CON 0x1D<7:6>)
bits. The CCAFAIL (TXSTAT 0x24<5>) bit = 1 indicates
if the failed transmission was due to the channel busy
(CSMA-CA timed out). The TXG1FNT (TXSTAT
0x24<3>) or TXG2FNT (TXSTAT 0x24<4>) bit = 1
indicates if TX GTSx FIFO transmission failed due to
not enough time to transmit in the guaranteed time slot.
DS39776B-page 124
Preliminary
© 2008 Microchip Technology Inc.