CC2550_06 Datasheet, PDF (21/55 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transmitter

CC2550
13.3 Packet Handling in Transmit Mode
The payload that is to be transmitted must be
written into the TX FIFO. The first byte written
must be the length byte when variable packet
length is enabled. The length byte has a value
equal to the payload of the packet (including
the optional address byte). If fixed packet
length is enabled, then the first byte written to
the TX FIFO is interpreted as the destination
address, if this feature is enabled in the device
that receives the packet.
The modulator will first send the programmed
number of preamble bytes. If data is available
in the TX FIFO, the modulator will send the
two-byte (optionally 4-byte) sync word and
then the payload in the TX FIFO. If CRC is
enabled, the checksum is calculated over all
the data pulled from the TX FIFO and the
result is sent as two extra bytes at the end of
the payload data.
If whitening is enabled, the length byte,
payload data and the two CRC bytes will be
whitened. This is done before the optional
FEC/Interleaver stage. Whitening is enabled
by setting PKTCTRL0.WHITE_DATA=1.
If FEC/Interleaving is enabled, the length byte,
payload data and the two CRC bytes will be
scrambled by the interleaver, and FEC
encoded before being modulated.
14 Modulation Formats
CC2550 supports amplitude, frequency and
phase shift modulation formats. The desired
modulation format is set in the
MDMCFG2.MOD_FORMAT register.
Optionally, the data stream can be Manchester
coded by the modulator. This option is enabled
by setting MDMCFG2.MANCHESTER_EN=1.
Manchester encoding is not supported at the
same time as using the FEC/Interleaver
option.
14.1 Frequency Shift Keying
FSK can optionally be shaped by a Gaussian
filter with BT=1, producing a GFSK modulated
signal.
The frequency deviation is programmed with
the DEVIATION_M and DEVIATION_E values
in the DEVIATN register. The value has an
exponent/mantissa form, and the resultant
deviation is given by:
f _dev
=
f _xosc
2¹⁷
⋅ (8 + DEVIATION _ M ) ⋅ 2^{DEVIATION _ E}
The symbol encoding is shown in Table 17.
Format
FSK\GFSK
Symbol
‘0’
‘1’
Coding
– Deviation
+ Deviation
Table 17: Symbol encoding for FSK
modulation
14.2 Minimum Shift Keying
When using MSK¹, the complete transmission
(preamble, sync word and payload) will be
MSK modulated.
Phase shifts are performed with a constant
transition time.
The fraction of a symbol period used to
change the phase can be modified with the
DEVIATN.DEVIATION_M setting. This is
equivalent to changing the shaping of the
symbol.
The MSK modulation format implemented in
CC2550 inverts the sync word and data
compared to e.g. signal generators.
14.3 Amplitude Modulation
The supported amplitude modulation On-Off
Keying (OOK) simply turns on or off the PA to
modulate 1 and 0 respectively.
1 _{Identical to offset QPSK with half-sine}
shaping (data coding may differ)
PRELIMINARY Data Sheet (Rev.1.2) SWRS039A
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