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Length Byte
n
MPDU
MPDU
1
Correlation Value (Unsigned)
0
1
2
3
4
5
6
7
SRCRESINDEX
0
1
2
3
4
5
6
7
RSSI (Signed 2s Complement)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Data in RXFIFO
AUTOCRC
= 0
MPDU
2
FCS
2
FCS
1
MPDU
n–2
• • • •
FRMCTRL0
Settings
AUTOCRC
APPEND_DATA_MODE
= 1 and
= 0
AUTOCRC
APPEND_DATA_MODE
= 1 and
= 1
CRC
OK
CRC
OK
RSSI (Signed 2s Complement)
M0114-01
2
1
2
MAC Header (MHR)
Bytes:
1
1
4
Preamble
Sequence
Start-of-Frame
Delimiter
(SFD)
Frame
Length
Frame
Control Field
(FCF)
Data
Sequence
Number
Frame Check
Sequence
(FCS)
MAC Footer
(MFR)
PHY Header
(PHR)
Synchronization Header
(SHR)
M0115-01
Receive Mode
23.9.7 Frame-Check Sequence
In receive mode, the FCS is verified by hardware if
FRMCTRL0.AUTOCRC
is enabled. The user is normally
only interested in the correctness of the FCS, not the FCS sequence itself. The FCS sequence itself is
therefore not written to the RXFIFO during receive. Instead, when
FRMCTRL0.AUTOCRC
is set, the two
FCS bytes are replaced by other more-useful values. The values that are substituted for the FCS
sequence are configurable in the
FRMCTRL0
register.
Figure 23-15. Data in RXFIFO for Different Settings
Field Descriptions:
•
The RSSI value is measured over the first eight symbols following the SFD.
•
The CRC_OK bit indicates whether the FCS is correct (1) or incorrect (0). When incorrect, software is
responsible for discarding the frame.
•
The correlation value is the average correlation value over the first eight symbols following the SFD.
•
SRCRESINDEX is the same value that is written to RAM after completion of source address matching.
Calculation of the LQI value used by IEEE 802.15.4 is described in
23.9.8 Acknowledgement Transmission
The radio includes hardware support for acknowledgment transmission after successful frame reception
(i.e., the FCS of the received frame must be correct).
shows the format of the
acknowledgment frame.
Figure 23-16. Acknowledge Frame Format
There are three variable fields in the generated acknowledgment frame:
•
The pending bit, which may be controlled with command strobes and the AUTOPEND feature (in the
FCF field)
•
The data sequence number (DSN), which is taken automatically from the last received frame
•
The FCS, which is given implicitly
241
SWRU191C
–
April 2009
–
Revised January 2012
CC253x Radio
Copyright
©
2009
–
2012, Texas Instruments Incorporated