CC2550-RTY1 datasheet(21/55 Pages) TI

21 / 55 page

CC2550

PRELIMINARY Data Sheet (Rev.1.2)

SWRS039A

Page 21 of 54

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.

Modulation Formats

CC2550 supports amplitude, frequency and

phase shift modulation formats. The desired

modulation

format

set

the

MDMCFG2.MOD_FORMAT

Optionally, the data stream can be Manchester

coded by the modulator. This option is enabled

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:

DEVIATION

xosc

dev

DEVIATION

)

(

⋅

The symbol encoding is shown in Table 17.

Format

Symbol

Coding

FSK\GFSK

‘0’

– Deviation

‘1’

+ Deviation

Table 17: Symbol encoding for FSK

modulation

14.2

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

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.

Identical to offset QPSK with half-sine

shaping (data coding may differ)

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