SX1231-31SKB868-EVAL Semtech, SX1231-31SKB868-EVAL Datasheet - Page 58

• Manufacturer Part Number: SX1231-31SKB868-EVAL
• Description: development tool usb kit for sx1231 transceiver...
• Manufacturer: Semtech

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
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.
Rev 4 - Nov 2010
ADVANCED COMMUNICATIONS & SENSING
RF chips @ BR
User/NRZ bits
Manchester OFF
User/NRZ bits
Manchester ON
Only one of the two methods should be enabled at a time.
data input
X
15
...
...
...
X
14
1
1
1
1/BR
1
1
1
X
13
Figure 35. Manchester Encoding/Decoding
...Sync
1
1
1
Figure 34. CRC Implementation
0
0
0
X
12
1
1
1
CRC Polynomial =X
0
0
0
0
0
0
Page 58
X
11
1
1
1
0
0
* * *
1/BR
0
0
16
+ X
0
1
1
12
X
5
+ X
0
0
Payload...
5
+ 1
0
1
1
1
1
X
1
4
0
0
* * *
1
1
1
DATASHEET
0
0
www.semtech.com
SX1231
X
0
...
...
...
t