SM1211E915TOPIC Semtech, SM1211E915TOPIC Datasheet - Page 54

• Manufacturer Part Number: SM1211E915TOPIC
• Description: KIT PICTAIL EXT FOR SX1211
• Manufacturer: Semtech
• Type: Transceiver, UHFr

Specifications of SM1211E915TOPIC

• Frequency: 915MHz
• For Use With/related Products: SX1211
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 MCParam_BR (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.
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. Comparing to Manchester technique it has the advantage of keeping NRZ datarate i.e. actual
bit rate is not halved.
The whitening/de-whitening process is enabled by setting bit PKTParam_Whitening_on. A 9-bit LFSR is used to
generate a random sequence. The payload and 2-byte CRC checksum is then XORed with this random sequence
as shown in Figure 47. The data is de-whitened on the receiver side by XORing with the same random sequence.
Payload whitening/de-whitening is thus made transparent for the user, who still provides/retrieves NRZ data to/from
the FIFO.
Tables below give the description of the interrupts available in Packet mode.
Rev 7 – Sept 2
ADVANCED COMMUNICATIONS & SENSING
RF chips @ BR
User/NRZ bits
Manchester OFF
User/NRZ bits
Manchester ON
X
5.5.7. Interrupt Signal Mapping
8
nd
, 2008
5.5.6.2. Data Whitening
X
...
...
...
7
1
1
1
1/BR
1
1
1
X
6
...Sync
1
1
1
Figure 46: Manchester Encoding/Decoding
0
0
0
1
1
1
X
Figure 47: Data Whitening
L F S R P o ly n o m ia l = X
5
0
0
0
0
0
0
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1
1
X
T ran sm it d ata
1
4
0
0
1/BR
0
0
0
9
+ X
X
1
1
3
5
+ 1
0
0
Payload...
0
1
1
X
2
1
1
1
0
0
X
1
1
1
W hite ne d d ata
1
www.semtech.com
0
0
SX1211
X
...
...
...
0
t