CC2500 datasheet(29/76 Pages) TI

29 / 76 page

CC2500

Preliminary Data Sheet (rev.1.1.)

SWRS040

Page 29 of 77

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

set

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:

DEVIATION

xosc

dev

DEVIATION

)

(

⋅

The symbol encoding is shown in Table 23.

Format

Symbol

Coding

2-FSK/GFSK

‘0’

– Deviation

‘1’

+ Deviation

Table 23: Symbol encoding for FSK

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. 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

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.

Identical to offset QPSK with half-sine

shaping (data coding may differ)

CC2500 Datasheet(PDF) 29 Page - Texas Instruments

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