MRF39RA datasheet(40/72 Pages) MICROCHIP

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MRF39RA

DS40001778B-page 40

 2015 Microchip Technology Inc.

4.5.7

DC-FREE DATA MECHANISMS

The received payload can be de-whitened or

automatically Manchester-decoded in the MRF39RA

packet handler.

4.5.7.1

Manchester Decoding

Manchester decoding is enabled if DcFree = 01 and it

can only be used in Packet mode.

The Manchester data is decoded to NRZ code by

decoding ‘10' as '1' and ‘01‘ as '0'.

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 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 decoding is thus made transparent for the

user, who still retrieves NRZ data from the FIFO.

FIGURE 4-13:

MANCHESTER DECODING

4.5.7.2

Data De-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. Compared to the

Manchester technique it has the advantage of keeping

the NRZ data rate (i.e., the actual bit rate is not halved).

The de-whitening process is enabled if DcFree = 10.

The data, including payload and 2-byte CRC

checksum, is de-whitened by XORing it with a random

sequence generated in a 9-bit LFSR as shown in

Figure 4-14.

Payload de-whitening is thus made transparent for the

user, who still retrieves NRZ data from the FIFO.

FIGURE 4-14:

DATA DE-WHITENING

Note:

Only one of the two methods must be

enabled at a time.

...Sync

Payload...

RF chips @ BR

...

User/NRZ bits

Manchester OFF

...

User/NRZ bits

Manchester ON

...

1/BR

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