CC2500 Datasheet, PDF (29/76 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
enabled, the packet handler computes CRC
and matches it with the appended CRC
checksum.
At the end of the payload, the packet handler
will optionally write two extra packet status
bytes that contain CRC status, link quality
indication and RSSI value.
16 Modulation Formats
CC2500 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. Manchester
coding can be used with the 2-ary modulation
formats (2-FSK, GFSK, OOK and MSK).
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:
f _dev
=
f _xosc
2¹⁷
⋅ (8 + DEVIATION _ M ) ⋅ 2^{DEVIATION _ E}
The symbol encoding is shown in Table 23.
Format
2-FSK/GFSK
Symbol
‘0’
‘1’
Coding
– Deviation
+ Deviation
Table 23: Symbol encoding for FSK
modulation
16.2 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. This means that the rate of
change for the 180-degree transition is twice
that of the 90-degree transition.
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. Setting DEVIATN.DEVIATION_M=7
will generate a standard shaped MSK signal.
The MSK modulation format implemented in
CC2500 inverts the sync word and data
compared to e.g. signal generators.
16.3 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.1.1.) SWRS040
Page 29 of 77