Data Sheet

CC1101
SWRS061B Page 35 of 93
MISO line each time a header byte, data byte,
or command strobe is sent on the SPI bus.
It is recommended to employ an interrupt
driven solution as high rate SPI polling will
reduce the RX sensitivity. Furthermore, as
explained in Section 10.3 and the
CC1101
Errata Notes [1], when using SPI polling there
is a small, but finite, probability that a single
read from registers PKTSTATUS , RXBYTES
and TXBYTES is being corrupt. The same is
the case when reading the chip status byte.
Refer to the TI website for SW examples ([8]
and [9]).
16 Modulation Formats
CC1101 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 and decoded by the
demodulator. 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.
16.1 Frequency Shift Keying
2-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:
EDEVIATION
xosc
dev
MDEVIATION
f
f
_
17
2)_8(
2
⋅+⋅=
The symbol encoding is shown in Table 23.
Format Symbol Coding
2-FSK/GFSK ‘0’ – Deviation
‘1’ + Deviation
Table 23: Symbol Encoding for 2-FSK/GFSK
Modulation
16.2 Minimum Shift Keying
When using MSK
1
, 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
CC1101 inverts the sync word and data
compared to e.g. signal generators.
16.3 Amplitude Modulation
CC1101 supports two different forms of
amplitude modulation: On-Off Keying (OOK)
and Amplitude Shift Keying (ASK).
OOK modulation simply turns on or off the PA
to modulate 1 and 0 respectively.
The ASK variant supported by the
CC1101
allows programming of the modulation depth
(the difference between 1 and 0), and shaping
of the pulse amplitude. Pulse shaping will
produce a more bandwidth constrained output
spectrum.
1
Identical to offset QPSK with half-sine
shaping (data coding may differ)