CC2420 Chipcon AS, CC2420 Datasheet - Page 34

• Manufacturer Part Number: CC2420
• Description: 2.4 GHz RF Transceiver for IEEE 802.15.4 and ZigBee
• Manufacturer: Chipcon AS

The FCS polynomial is [1]:
The
shown in Figure 18. 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.
Instead, when MODEMCTRL0.AUTOCRC is
set the two FCS bytes are replaced by the
RSSI value, average correlation value
RF Data Buffering
CC2420
transmit and receive modes, as set in the
MDMCTRL1.TX_MODE
MDMCTRL1.RX_MODE
Buffered mode (mode 0) will be used for
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
(LSB
Data
input
first)
Data in RXFIFO
CC2420
Figure 18.
can be configured for different
r0
x
hardware implementation is
16
r1
Length byte
Figure 19. Data in RXFIFO when MDMCTRL0.AUTOCRC is set
+ x
CC2420
12
r2
n
+ x
5
r3
Frame Check Sequence (FCS) hardware implementation [1]
+ 1
control
MPDU
r4
1
r5
bits.
and
MPDU
r6
2
r7
SmartRF
Bit number
(used for LQI) and CRC OK/not OK. This
is illustrated in Figure 19.
The first FCS byte is replaced by the 8-bit
RSSI value. See the RSSI section on
page 45 for details.
The 7 least significant bits in the last FCS
byte
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 46 for
details.
The most significant bit in the last byte of
each frame is set high if the CRC of the
received
otherwise.
normal operation of
modes are available for test purposes.
r8
r9
are
MPDU
r10
CRC
OK
frame
7
replaced
MPDU
6
r11
Correlation value (unsigned)
®
is
n-2
5
r12
CC2420
correct
by
CC2420
4
(signed)
r13
RSSI
the
, while other
3
r14
Page 34 of 85
and
2
average
CRC / Corr
r15
1
low
0