Data Sheet

Page 59
RFM69HCW
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ADVANCED COMMUNICATIONS & SENSING DATASHEET
5.5.8.2. Data Whitening
Another technique called whitening or scrambling is widely used for randomizing the user data before radio transmission.
The data is whitened using a random sequence on the Tx side and de-whitened on the Rx side using the same sequence.
Comparing to Manchester technique it has the advantage of keeping NRZ data rate i.e. actual bit rate is not halved.
The whitening/de-whitening process is enabled if DcFree = 10. A 9-bit LFSR is used to generate a random sequence. The
payload and 2-byte CRC checksum is then XORed with this random sequence as shown below. The data is de-whitened
on the receiver side by XORing with the same random sequence.
Payload whitening/de-whitening is thus made transparent for the user, who still provides/retrieves NRZ data to/from the
FIFO.
LFS R P o ly nom ia l =X
9
+ X
5
+ 1
X
8
X
7
X
6
X
5
X
4
X
3
X
2
X
1
X
0
Tra n s m it d a ta
W
h iten ed da ta
Figure 37. Data Whitening