CC1110Fx / CC1111Fx
If the system can expect the transmission to
have started when enabling the receiver, the
MCSM2.RX_TIME_RSSIfunction can be used.
The radio controller will then terminate RX if
the first valid carrier sense sample indicates no
carrier (RSSI below threshold). See Section
14.10.4 on page 197 for details on Carrier
Sense.
14.12.3 RX Termination Timer
CC1110Fx/CC1111Fx has optional functions for
automatic termination of RX after
a
programmable time. The termination timer
starts when in RX state. The timeout is
programmable with the MCSM2.RX_TIME
setting. When the timer expires, the radio
controller will check the condition for staying in
RX; if the condition is not met, RX will
terminate.
For ASK/OOK modulation, lack of carrier
sense is only considered valid after eight
symbol
periods.
Thus,
the
MCSM2.RX_TIME_RSSI function can be used
in ASK/OOK mode when the distance between
“1” symbols is 8 or less.
The programmable conditions are:
•
•
MCSM2.RX_TIME_QUAL=0:
receive if sync word has been found
MCSM2.RX_TIME_QUAL=1:
receive if sync word has been found or
preamble quality is above threshold
(PQT)
Continue
If RX terminates due to no carrier sense when
the MCSM2.RX_TIME_RSSI function is used,
or if no sync word was found when using the
MCSM2.RX_TIMEtimeout function, the chip will
always go back to IDLE.
Continue
14.13 Frequency Programming
The frequency programming
CC1110Fx/CC1111Fx is designed to minimize the
programming needed in a channel-oriented
system.
in
The base or start frequency is set by the 24 bit
frequency word located in the FREQ2, FREQ1
and FREQ0registers. This word will typically be
set to the centre of the lowest channel
frequency that is to be used.
To set up a system with channel numbers, the
desired channel spacing is programmed with
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:
the
MDMCFG0.CHANSPC_M
and
MDMCFG1.CHANSPC_E registers. The channel
spacing registers are mantissa and exponent
respectively.
fref
216
fcarrier
=
⋅
(
FREQ + CHAN ⋅
(
(256 + CHANSPC _ M ) ⋅ 2CHANSPC _ E−2 ))
With a reference frequency, fRef, equal to 26
MHz, the maximum channel spacing is 405
kHz. To get e.g. 1 MHz channel spacing one
solution is to use 333 kHz channel spacing and
select each third channel in CHANNR.CHAN.
Note that the SmartRF® Studio software [9]
automatically calculates the optimum register
setting based on channel spacing and channel
filter bandwidth.
If any frequency programming register is
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.
The preferred IF frequency is programmed
with the FSCTRL1.FREQ_IF register. The IF
frequency is given by:
fref
210
fIF
=
⋅ FREQ _ IF
14.14 VCO
The VCO is completely integrated on-chip.
synthesizer self-calibration circuitry. This
calibration should be done regularly, and must
be performed after turning on power and
before using a new frequency (or channel).
The number of fRef periods for completing the
PLL calibration is given in Table 72 on page
202.
14.14.1 VCO and PLL Self-Calibration
The VCO characteristics will vary with
temperature and supply voltage changes, as
well as the desired operating frequency. In
order
to
ensure
reliable
operation,
CC1110Fx/CC1111Fx
includes
frequency
SWRS033E
Page 203 of 239
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