CC1010-RTY1 datasheet(107/152 Pages) TI

107 / 152 page

CC1010

SWRS047

Page 107 of 152

17.12 Frequency programming

RX mode:

LO (low-side)

LO (high-side)

(Receive frequency)

TX mode:

(Center frequency)

sep

(Lower FSK

frequency)

(Upper FSK

frequency)

vco

Figure 33, Relation between fvco, fif, and LO frequency

The

frequency

synthesiser

(PLL)

controlled by the frequency word in the

configuration registers. There are two

frequency words, A and B, which can be

programmed to two different frequencies.

One of the frequency words can be used

for RX (local oscillator frequency) and

other for TX (transmitting frequency, f0).

This makes it possible to switch very fast

between RX mode and TX mode. They

can also be used for RX (or TX) on two

different channels. Selection of frequency

word A or B is performed by using the

RFMAIN.F_REG control bit.

The frequency word, FREQ, is 24 bits (3

bytes)

located

FREQ_2A:FREQ_1A:FREQ_0A

and

FREQ_2B:FREQ_1B:FREQ_0B for the A

and B word, respectively.

The FSK frequency separation (two times

the deviation), FSEP, is programmed in

the FSEP1:FSEP0 registers (11 bits).

The frequency word FREQ can be

calculated from:

16384

8192

⋅

TXDATA

FSEP

FREQ

ref

VCO

where TXDATA is 0 or 1 in transmit mode

depending

the

data

bit

transmitted. In receive mode TXDATA is

always 0.

The reference frequency fref is the crystal

oscillator clock divided by PLL.REFDIV, a

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