MRF89XA datasheet(86/140 Pages) MICROCHIP

86 / 140 page

MRF89XA

DS70000622D-page 86

Preliminary

 2010-2017 Microchip Technology Inc.

3.11.4

DC-FREE DATA MECHANISMS

The payload to be transmitted may contain long

sequences of ‘1’s and ‘0’s. These continuous

sequences introduce a DC bias in the transmitted

signal, which causes a non-uniform power distribution

spectrum over the occupied channel bandwidth. These

sequences also degrade the performance of the

demodulation and data, and clock recovery functions in

the receiver, which could further introduce data

dependencies in the normal operation of the

demodulator. System performance can be enhanced if

the payload bits are randomized to reduce DC biases

and increase the number of bit transitions. Therefore, it

is useful if the transmitted data is random and DC-free.

To handle such instances, two techniques are available

in the packet handler: Manchester encoding and Data

Whitening. However, only one of the two methods

should be enabled at a time.

3.11.4.1

Manchester Data Encoding

Manchester encoding/decoding is enabled by setting

the MCHSTREN bit (PLOADREG<7>) and can be

used in Packet mode only. The NRZ data is converted

to Manchester code by coding ‘1’ as ‘10’ and ‘0’ as ‘01’.

Figure 3-29 illustrates Manchester data encoding. NRZ

data is converted to Manchester by encoding the 1 bits

as 10 chip sequences, and the 0 bits as 01 chip

sequences. Manchester encoding guarantees DC-

balance and frequent data transitions in the encoded

data. The maximum Manchester chip rate corresponds

to the maximum bit rate given in the Transmitter

Electrical specifications in Table 5-6.

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 the preamble and Sync Word are kept

NRZ. However, the chip rate from the preamble to CRC

is the same and defined by the BRVAL<6:0> bits

(BRSREG<6:0>) (Chip Rate = Bit Rate NRZ = 2 x Bit

Rate Manchester).

Therefore, Manchester encoding or decoding is made

transparent to the user who still provides or retrieves

NRZ data to or from the FIFO. See the Manchester

encoding or decoding bit pattern in Figure 3-30.

3.11.4.2

Data Whitening

Another technique called data 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 dewhitened on

the RX side using the same sequence. Compared to

the Manchester technique, it has the advantage of

retaining the NRZ data rate (that is, actual bit rate is not

halved).

The whitening or dewhitening process is enabled by

setting the WHITEN1 bit (PKTCREG<4>). A 9-bit

Linear Feedback Shift Register (LFSR) is used to

generate a random sequence. The payload and 2-byte

CRC checksum is then XORed with this random

sequence as illustrated in Figure 3-31. The data is

dewhitened on the receiver side by XORing with the

same random sequence.

Payload whitening or dewhitening is made transparent

to the user who still provides or retrieves NRZ data to

or from the FIFO.

FIGURE 3-29:

MANCHESTER DATA ENCODING

FIGURE 3-30:

MANCHESTER ENCODING/DECODING

...Sync

Payload...

RF chips @ BR

...

0 0

1 0

...

User/NRZ bits

Manchester OFF

...

0 0

1 0

...

User/NRZ bits

Manchester ON

...

1 0

0 1

...

1/BR 1/

MRF89XA Datasheet(PDF) 86 Page - Microchip Technology

MRF89XA Datasheet(HTML) 86 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL