Texas Instruments CC112 Series, User Manual, Page: 64 / 109

CC112X/CC1175
SWRU295C Page 64 of 108
8.9.1 Antenna Diversity Features
The device supports antenna diversity by controlling an external RF switch using the
ANTENNA_SELECT
control signal available on GPIO (
IOCFGx.GPIOx_CFG = ANTENNA_SELECT
(36)).
The device will remember the last antenna used (when not entering SLEEP mode
18
) and use the last
antenna for the next RX or TX transition. Staying with the same antenna will make sure:
In RX, that the last antenna used for good reception will be the first one to be checked
(minimize time for the next reception)
In TX, the device will transmit acknowledge with the same antenna that received the packet.
8.10 Random Number Generator
A random number generator is available and can be enabled by setting
RNDGEN.RNDGEN_EN = 1
. A
random number can be read from
RNDGEN.RNDGEN_VALUE
in any state, but the number will be
further randomized when in RX by XORing the feedback with receiver noise.
8.11 Frequency Synthesizer Configuration
If any frequency programming registers are altered when the frequency synthesizer is running, the
synthesizer may give an undesired response. Hence, the frequency programming should only be
updated when the radio is in the IDLE state.
8.12 RF Programming
RF programming in
CC112X
is given by two factors; the VCO frequency programming and the LO
divider programming (RF band selection). The relation is given in Equation 23 below.
Divider LO
VCO
RF
f
f
Equation 23: Radio Frequency
The VCO frequency is given by the 24 bit (unsigned) frequency word FREQ located in the
FREQ2
,
FREQ1
, and
FREQ0
registers. There is also a possibility to perform VCO frequency offset
programming, given by the 16 bit (signed) frequency offset word FREQOFF located in the
FREQOFF1
and
FREQOFF0
registers. This is intended to adjust for crystal intolerance or fine adjustments of the
RF programming.
XOSC XOSC VCO
f
FREQOFF
f
FREQ
f
18 16
2 2
Equation 24: VCO Frequency
Note that the FREQOFF programming and FREQOFF_EST (found in
FREQOFF_EST1
and
FREQOFF_EST0
) have identical formats hence the frequency estimate can be accumulated directly to
the FREQOFF programming. This can be done either manually or automatically through the
SAFC
command strobe. A
SAFC
command strobe can be issued in any state but does not take effect until
the next time the radio enters active mode (TX or RX).
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In SLEEP mode the GDIOx pin will be hardwired to 0 or 1 depending on which GDIO pin is used
and what the value of
IOCFGx_GPIOx_INV
is. Please see Section 3.4 for more details.