AT86RF230_09 ATMEL [ATMEL Corporation], AT86RF230_09 Datasheet - Page 48

• Manufacturer Part Number: AT86RF230_09
• Description: Low Power 2.4 GHz Transceiver for ZigBee, IEEE 802.15.4, 6LoWPAN, RF4CE and ISM
• Manufacturer: ATMEL [ATMEL Corporation]

8.1.2.6 MAC Footer (MFR) Fields
8.2 Frame Check Sequence (FCS)
8.2.1.1 Overview
8.2.2 CRC calculation
48
AT86RF230
The MAC footer consists of a two-octet frame checksum (FCS). The AT86RF230 can
generate and evaluate this FCS automatically, for details refer to section 8.2.
The frame check sequence main features are:
• Indicates bit errors, based on a cyclic redundancy check (CRC) of length 16 bit
• Uses International Telecommunication Union (ITU) CRC polynomial
• Automatically evaluated during reception
• Can be automatically generated during transmission
The FCS is intended for use at the MAC level to detect corrupted frames. It is computed
by applying an ITU CRC polynomial to all transferred bytes following the length field
(MHR and MSDU fields). The frame check sequence has a length of 16 bit and is
located in the last two bytes of a frame (MAC footer, see Figure 8-2).
The AT86RF230 applies an FCS check on each received frame. The FCS check result
is stored to register bit RX_CRC_VALID in register 0x06 (PHY_RSSI). On transmit the
radio transceiver can be configured to autonomously compute and append the FCS
bytes.
The CRC polynomial used in IEEE 802.15.4-2003 networks is defined by
The FCS shall be calculated for transmission using the following algorithm:
Let
be the polynomial representing the sequence of bits for which the checksum is to be
computed. Multiply M(x) by x
Divide N(x) modulo 2 by the generator polynomial, G
polynomial,
The FCS field is given by the coefficients of the remainder polynomial, R(x) .
Example:
Considering a 5 octet ACK frame. The MHR field consists of
The leftmost bit (b
The leftmost bit (r
0100 0000 0000 0000 0101 0110.
0010 0111 1001 1110.
G
M
R
N
16
(
(
(
x
(
x
x
)
x
)
)
)
=
=
=
=
M
b
r
0
0
0
) is transmitted first in time.
x
0
) is transmitted first in time. The FCS would be following
x
(
16
x
15
x
k
)
−
+
+
1
⋅
x
x
+
x r
16
1
12
b
.
1
14
+
x
16
k
+
, giving the polynomial
x
−
5
2
...
+
+
+
1
K
r
.
14
+
x
b
+
k
−
r
15
2
x
+
b
k
−
1
16
(x) , to obtain the remainder
5131E-MCU Wireless-02/09