Si1000/1/2/3/4/5
Manchester
Whitening
CRC
CRC
(Over data only)
Header/
Address
PK
Length
Preamble
Sync
CRC
Data
Figure 23.17. Operation of Data Whitening, Manchester Encoding, and CRC
Data before Manchester
1
1
1
1
1
1
1
1
0
0
0
1
0
Preamble = 0xFF
First 4bits of the synch. word = 0x2
Data after Machester ( manppol = 1, enmaninv = 0)
Data after Machester ( manppol = 1, enmaninv = 1)
Data before Manchester
0
0
0
0
0
0
0
0
0
0
0
1
0
Preamble = 0x00
First 4bits of the synch. word = 0x2
Data after Machester ( manppol = 0, enmaninv = 0)
Data after Machester ( manppol = 0, enmaninv = 1)
Figure 23.18. Manchester Coding Example
23.6.6. Preamble Detector
The EZRadioPRO transceiver has integrated automatic preamble detection. The preamble length is con-
figurable from 1–255 bytes using the prealen[7:0] field in "Register 33h. Header Control 2" and "Register
34h. Preamble Length", as described in “23.6.2. Packet Configuration” . The preamble detection threshold,
preath[4:0] as set in "Register 35h. Preamble Detection Control 1", is in units of 4 bits. The preamble
detector searches for a preamble pattern with a length of preath[4:0].
If a false preamble detect occurs, the receiver will continuing searching for the preamble when no sync
word is detected. Once preamble is detected (false or real) then the part will then start searching for sync.
If no sync occurs then a timeout will occur and the device will initiate search for preamble again. The time-
out period is defined as the sync word length plus four bits and will start after a non-preamble pattern is
recognized after a valid preamble detection. The preamble detector output may be programmed onto one
of the GPIO or read in the interrupt status registers.
23.6.7. Preamble Length
The preamble detection threshold determines the number of valid preamble bits the radio must receive to
qualify a valid preamble. The preamble threshold should be adjusted depending on the nature of the appli-
cation. The required preamble length threshold will depend on when receive mode is entered in relation to
the start of the transmitted packet and the length of the transmit preamble. With a shorter than recom-
mended preamble detection threshold the probability of false detection is directly related to how long the
receiver operates on noise before the transmit preamble is received. False detection on noise may cause
the actual packet to be missed. The preamble detection threshold is programmed in register 35h. For most
applications with a preamble length longer than 32 bits the default value of 20 is recommended for the pre-
266
Rev. 1.0
SILICON [ SILICON ]
