MRF24XA_15 Datasheet, PDF (151/258 Pages) Microchip Technology – Low-Power, 2.4 GHz ISM-Band IEEE 802.15.4™ RF

MRF24XA
FIGURE 5-10:
CCM* DECRYPTION AND DE-AUTHENTICATION OPERATION (RX)^{(1, 2, 3)}
Received
from the air
Length
MHR
Encrypted Payload
Encrypted
Tag
CRC
Length
MHR
CRC Check
Encrypted Payload
Encrypted
Tag
CRC
Decryption
Length
MHR
Data/CMD Payload
Tag
CRC
MIC Compare
RX Buffer
Length
MHR
Data/CMD Payload
Tag
CRC
Exception Handling:
RXTAGIF: Receiver Decryption/Authentication Failure Interrupt Flag
Set by the device when decryption/authentication finished with error.
Note 1:
2:
3:
The Length field above refers to the total number of octets as reported by the Baseband, and therefore
includes the Tag (MIC), but excludes any RSV octets.
If present, RSV octets are placed after the Tag, as these are only received when the complete frame is
received. It is the responsibility of software to determine the address of the RSV in the buffer (RSV
Address = Length + 1), and to discard/ignore the Tag octets.
The Message and Tag decryption operations do not depend on each other, and may be computed in
any order. All other factors being equal, the Tag decryption operation must be performed first, as it
uses the starting counter value.
 2015 Microchip Technology Inc.
Preliminary
DS70005023C-page 151