MC33596_10 Datasheet, PDF (15/70 Pages) Freescale Semiconductor, Inc – PLL Tuned UHF Receiver for Data Transfer Applications

Receive Mode
DME = 0: The data manager is disabled. The SPI is deselected. Raw data is sent directly on the MOSI line,
while SCLK remains at the low level.
Manchester coding is defined as follows: data is sent during the first half-bit; and the complement of the
data is sent during the second half-bit. The signal average value is constant.
0
1
0
0
1
1
0
ORIGINAL
DATA
MANCHESTER
CODED DATA
Figure 6. Example of Manchester Coding
Clock recovery can be extracted from the data stream itself. To achieve correct clock recovery,
Manchester-coded data must have a duty cycle between 47% and 53%.
11.2.3 Frame Format
A complete telegram includes the following sequences: a preamble, an identifier (ID), a header, the
message, and an end-of-message (EOM).
PREAMBLE ID ID ID ID HEADER DATA ………… EOM
Figure 7. Example of Frame Format
These bit sequences are described below.
11.2.3.1 Preamble
A preamble is required before the first ID detected. It enables:
— In the case of OOK modulation, the AGC to settle, and the data slicer reference voltage to
settle if DSREF = 1
— In the case of FSK modulation, the data slicer reference voltage to settle
— The data manager to start clock recovery
No preamble is needed in case of several IDs are sent as shown in Figure 8. The ID field must be greater
than two IDs. The first ID will have the same function as the preamble, and the second ID will have the
same function as the single ID.
... ID ID ID ID ID ID HEADER DATA …………
Figure 8. Example of Frame with Several IDs, No Preamble Needed
For both cases, the preamble content must be defined carefully, to ensure that it will not be decoded as the
ID or the header. Figure 9 defines the different preamble in OOK and FSK modulation.
MC33596 Data Sheet, Rev. 4
Freescale Semiconductor
15