EM2420 ETC [List of Unclassifed Manufacturers], EM2420 Datasheet - Page 36

• Manufacturer Part Number: EM2420
• Description: 2.4 GHz IEEE 802.15.4 / ZigBee RF Transceiver
• Manufacturer: ETC [List of Unclassifed Manufacturers]

EM2420
The FCS polynomial is [1]:
16
12
5
x
+ x
+ x
+ 1
The EM2420 hardware implementation is
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
(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 48 for details.
The 7 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
Ember Part Number: 120-0049-000C
EM2420 Datasheet
Page 36 of 89