RF69 datasheet(59/81 Pages) ETC2

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RF69

Page 58

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data input

CRC Polynomial =X16 + X12 + X5 + 1

X15

X14

X13

X12

X11

* * *

Figure 36. CRC Implementation

5.5.8. DC-Free Data Mechanisms

The payload to be transmitted may contain long sequences of 1's and 0's, which introduces a DC bias in the transmitted

signal. The radio signal thus produced has a non uniform power distribution over the occupied channel bandwidth. It also

introduces data dependencies in the normal operation of the demodulator. Thus it is useful if the transmitted data is random

and DC free.

For such purposes, two techniques are made available in the packet handler: Manchester encoding and data whitening.

Note

Only one of the two methods should be enabled at a time.

5.5.8.1. Manchester Encoding

Manchester encoding/decoding is enabled if DcFree = 01 and can only be used in Packet mode.

The NRZ data is converted to Manchester code by coding '1' as "10" and '0' as "01".

In this case, the maximum chip rate is the maximum bit rate given in the specifications section and the actual bit rate is half

the chip rate.

Manchester encoding and decoding is only applied to the payload and CRC checksum while preamble and Sync word are

kept NRZ. However, the chip rate from preamble to CRC is the same and defined by BitRate in RegBitRate (Chip Rate =

Bit Rate NRZ = 2 x Bit Rate Manchester).

Manchester encoding/decoding is thus made transparent for the user, who still provides/retrieves NRZ data to/from the

FIFO

1/BR ...Sync

1/BR

Payload...

RF chips @ BR

...

User/NRZ bits

Manchester OFF

...

User/NRZ bits

Manchester ON

...

Figure 37. Manchester Encoding/Decoding

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