CC115LRGPR datasheet(34/74 Pages) TI2

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XOSC

FREQ _ IF

CHANSPC _ 2 2

XOSC

carrier

(FREQ

CHAN ((256

CHANSPC _ M) 2

))

CC115L

SWRS105B – MAY 2011 – REVISED JUNE 2014

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5.12 Frequency Programming

The frequency programming in CC115L is designed to minimize the programming needed when changing

frequency.

To set up a system with channel numbers, the desired channel spacing is programmed with the

MDMCFG0.CHANSPC_M and MDMCFG1.CHANSPC_E registers. The channel spacing registers are

mantissa and exponent respectively. The base or start frequency is set by the 24 bit frequency word

located in the FREQ2, FREQ1, and FREQ0 registers. This word will typically be set to the center of the

lowest channel frequency that is to be used.

The desired channel number is programmed with the 8-bit channel number register, CHANNR.CHAN,

which is multiplied by the channel offset. The resultant carrier frequency is given by:

(5)

With a 26 MHz crystal the maximum channel spacing is 405 kHz. To get that is, 1-MHz channel spacing,

one solution is to use 333 kHz channel spacing and select each third channel in CHANNR.CHAN.

The preferred IF frequency is programmed with the FSCTRL1.FREQ_IF register. The IF frequency is

given by:

(6)

If any frequency programming register is altered when the frequency synthesizer is running, the

synthesizer may give an undesired response. Hence, the frequency should only be updated when the

radio is in the IDLE state.

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