CC2430 Datasheet, PDF (163/212 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
Radio : RF Data Buffering
The CC2430 hardware implementation is
shown in Figure 42. Please refer to [1] for
further details.
In transmit mode the FCS is appended at the
correct position defined by the length field. The
FCS is not written to the TXFIFO, but stored in
a separate 16-bit register.
In receive mode the FCS is verified by
hardware. 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.
and CRC OK/not OK. This is illustrated in
Figure 43.
The first FCS byte is replaced by the 8-bit
RSSI value. See the RSSI section on page
168 for details.
The seven least significant bits in the last FCS
byte are replaced by the average correlation
value of the 8 first symbols of the received
PHY header (length field) and PHY Service
Data Unit (PSDU). This correlation value may
be used as a basis for calculating the LQI. See
the Link Quality Indication section on page 168
for details.
Instead, when MDMCTRL0L.AUTOCRC is set
the two FCS bytes are replaced by the RSSI
value, average correlation value (used for LQI)
The most significant bit in the last byte of each
frame is set high if the CRC of the received
frame is correct and low otherwise.
Data
input
(LSB
first)
r0 r1 r2 r3
r4 r5 r6 r7 r8 r9 r10
r11 r12 r13 r14 r15
Figure 42: CC2430 Frame Check Sequence (FCS) hardware implementation [1]
Length byte
Data in RXFIFO
n
MPDU₁
MPDU₂
MPDU
MPDU_n-2
RSSI
(signed)
CRC / Corr
Bit number 7 6 5 4 3 2 1 0
CRC
OK
Correlation value (unsigned)
Figure 43: Data in RXFIFO when MDMCTRL0L.AUTOCRC is set
14.17 RF Data Buffering
CC2430 can be configured for different transmit
and receive modes, as set in the
MDMCTRL1L.TX_MODE
and
MDMCTRL1L.RX_MODE control bits. Buffered
14.17.1 Buffered transmit mode
In buffered transmit mode (TX_MODE=0), the
128 byte TXFIFO is used to buffer data before
transmission. A synchronization header is
automatically inserted before the length field
during transmission. The length field must
always be the first byte written to the transmit
buffer for all frames.
Writing one or multiple bytes to the TXFIFO is
described in the FIFO access section on page
157. A DMA transfer can be configured to
write transmit data to the TXFIFO.
mode (mode 0) will be used for normal
operation of CC2430, while other modes are
available for test purposes.
Transmission is enabled by issuing a STXON
or STXONCCA command strobe. See the Radio
control state machine section on page 166 for
an illustration of how the transmit command
strobes affect the state of CC2430. The
STXONCCA strobe is ignored if the channel is
busy. See section 14.25 on page 169 for
details on CCA.
The preamble sequence is started 12 symbol
periods after the transmit command strobe.
After the programmable start of frame delimiter
CC2430 Data Sheet (rev. 2.1) SWRS036F
Page 163 of 211