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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.
FRMCTRL0 Settings
AUTOCRC = 0
= 1 and
AUTOCRC
APPEND_DATA_MODE
= 1 and
AUTOCRC
APPEND_DATA_MODE
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
(that is, the FCS of the received frame must be correct).
acknowledgment frame.
Bytes:
4
Preamble
Sequence
Synchronization Header
(SHR)
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
230
CC253x Radio
Length Byte
MPDU
n
1
7
6
5
4
3
= 0
RSSI (Signed 2s Complement)
7
6
5
4
= 1
RSSI (Signed 2s Complement)
Figure 23-15. Data in RXFIFO for Different Settings
1
1
Start-of-Frame
Frame
Delimiter
Length
(SFD)
PHY Header
(PHR)
Figure 23-16. Acknowledge Frame Format
Copyright © 2009–2014, Texas Instruments Incorporated
Data in RXFIFO
MPDU
MPDU
MPDU
2
• • • •
2
1
0
7
6
CRC
Correlation Value (Unsigned)
OK
3
2
1
0
7
6
CRC
OK
Section
Figure 23-16
shows the format of the
2
Frame
Control Field
(FCF)
MAC Header (MHR)
FCS
FCS
n–2
1
2
5
4
3
2
1
0
5
4
3
2
1
0
SRCRESINDEX
M0114-01
23.10.4.
1
2
Frame Check
Data
Sequence
Sequence
(FCS)
Number
MAC Footer
(MFR)
SWRU191F – April 2009 – Revised April 2014
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www.ti.com
M0115-01
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