CC2430 Datasheet, PDF (175/234 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
14.15 MAC protocol data unit
The FCF, data sequence number and
address information follows the length field
as shown in Figure 45. Together with the
MAC data payload and Frame Check
Sequence, they form the MAC Protocol
Data Unit (MPDU).
The format of the FCF is shown in Figure
47. Please refer to [1] for details.
There is no hardware support for the data
sequence number, this field must be
inserted and verified by software.
CC2430 includes hardware address
recognition, as described in the Address
Recognition section on page 177.
Bits: 0-2
Frame
Type
3
Security
Enabled
4
Frame
Pending
5
Acknowledge
request
6
Intra
PAN
7-9
Reserved
10-11
Destination
addressing
mode
12-13
Reserved
Figure 47: Format of the Frame Control Field (FCF) [1]
14-15
Source
addressing
mode
14.16 Frame check sequence
A 2-byte frame check sequence (FCS)
follows the last MAC payload byte as
shown in Figure 45. The FCS is calculated
over the MPDU, i.e. the length field is not
part of the FCS. This field is automatically
generated and verified by hardware when
the RF register MDMCTRL0L.AUTOCRC
control bit is set. It is recommended to
always have this enabled, except possibly
for debug purposes. If cleared, CRC
generation and verification must be
performed by software.
The FCS polynomial is [1]:
x¹⁶ + x¹² + x⁵ + 1
The CC2430 hardware implementation is
shown in Figure 48. 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 MDMCTRL0L.AUTOCRC is
set the two FCS bytes are replaced by the
RSSI value, average correlation value
(used for LQI) and CRC OK/not OK. This
is illustrated in Figure 49.
The first FCS byte is replaced by the 8-bit
RSSI value. See the RSSI section on page
181 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 182 for
details.
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.
CC2430 PRELIMINARY Data Sheet (rev. 1.03) SWRS036A
Page 175 of 232