LLCC68 datasheet(41/106 Pages) SEMTECH

41 / 106 page

LLCC68

Data Sheet

Rev. 1.0

DS.LLCC68.W.APP

July 2019

41 of 106

Semtech

www.semtech.com

6.2.3.3 Setting the Packet Length or Node Address

The packet length and Node or Broadcast address are not considered part of the payload and they are added automatically

in hardware.

The packet length is added automatically in the packet when the packetType field is set to variable size in the command

SetPacketParam(...).

The node or broadcast address can be enabled by using the AddrComp field is in the command SetPacketParam(...). This

field allow the user to enable and select an additional packet filtering at the payload level.

6.2.3.4 Whitening

The whitening process is built around a 9-bit LFSR which is used to generate a random sequence and the payload (including

the payload length, the Node or Broadcast address and CRC checksum when needed) is then XORed with this random

sequence to generate the whitened payload. The data is de-whitened on the receiver side by XORing with the same

random sequence. This setup limits the number of consecutive 1’s or 0’s to 9. Note that the data whitening is only required

when the user data has high correlation with long strings of 0’s and 1’s. If the data is already random then the whitening is

not required. For example a random source generating the Transmit data, when whitened, could produce longer strings of

1’s and 0’s, thus it’s not required to randomize an already random sequence.

Figure 6-5: Data Whitening LFSR

The whitening is based around the 9-bit LFSR polynomial x^9+x^5+1. With this structure, the LSB at the output of the LFSR

is XORed with the MSB of the data.

At the initial stage, each flip-flop of the LFSR can be initialized through the registers at addresses 0x06B8 and 0x6B9.

Table 6-5: Whitening Initial Value

Whitening Initial Value

Default Value

Whitening initial value MSB

0x06B8

0x01

Whitening initial value LSB

0x06B9

0x00

X 7

X 6

X 5

X 4

X 3

X 2

X 1

X 0

X 8

LFS R P o ly nom ia l = X 9 + X 5 + 1

T ransm it data

W hitened data

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