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Exercise: Changing the frequency
It is obvious, that changing the RF frequency is a fundamental requirement of frequency hopping systems. Programming the RF frequency is done according chapter 9.1.2 of CC1200 Users Guide.
In detail, the HF $f_{RF}$ frequency is computed by:
$$ f_{RF}=\frac{f_{VCO}}{LO\ Divider} $$
where $f_{VCO}$ the frequency of the “Voltage Controlled Oscillator (VCO)” is
$$ f_{VCO} = \frac{FREQ}{2^{16}} . f_{XOSC} + \frac{FREQOFF}{2^{18}} . f_{XOSC}$$
In this two equations $f_{XOSC}$ is the crystal frequency of the TI boards and equal to $40 MHz$. LO Divider determines the frequency band of the CC1200 and will be programmed by the FSD_BANDSELECT part of the “Frequency Synthesizer Configuration” register (FS_CFG register).
FREQ is the 24 bit VCO frequency and computed by the FREQ0 (bits 16-23 of FREQ), FREQ1 (bits 8-16 of FREQ) and FREQ2 (bits 0-7 of FREQ) registers. FEQOFF is intended for fine tuning the RF frequency caused by tolerances of the crystal and can be neglected.
