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CC11x1-Q1
SWRS076B – 11-07-22-013 - APRIL 2009 – REVISED APRIL 2010
3.17 Frequency Programming
The frequency programming in CC11x1-Q1 is designed to minimize the programming needed in a
channel-oriented system.
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 is typically 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:
×
With a 26-MHz crystal the maximum channel spacing is 405 kHz. To get, for example, 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:
f
XOSC
f
FREQ_IF
=
´
IF
10
2
The SmartRF Studio software automatically calculates the optimum FSCTRL1.FREQ_IF
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.
3.18 VCO
The VCO is completely integrated on-chip.
52
Detailed Description
Overflow
margin
56 bytes
Underflow
margin
RXFIFO
Figure 3-20. Example of FIFOs at Threshold
×
×
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8 bytes
TXFIFO
NOTE
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