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LMX2571_15 Datasheet, PDF (36/61 Pages) Texas Instruments – LMX2571 Low-Power, High-Performance PLLatinum™ RF Synthesizer with FSKModulation
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LMX2571
SNAS654 – MARCH 2015
www.ti.com
In FSK SPI FAST mode, write the desired FSK steps directly to register R33, FSK_DEV_SPI_FAST. To enable
this mode, set
FSK_MODE_SEL1 = 1
FSK_MODE_SEL0 = 1
FSK_EN_F1 = 1
Table 34. FSK SPI FAST Mode Example
TIME
t0
t1
t2
…
t6
t7
…
FREQUENCY
DEVIATION
618.034 Hz
1618.034 Hz
2000 Hz
…
–1618.034 Hz
–2000 Hz
…
CORRESPONDING FSK
STEPS (1)
518
1357
1678
…
64178
63857
…
BINARY EQUIVALENT
0000 0010 0000 0110
0000 0101 0100 1101
0000 0110 1000 1110
…
1111 1010 1011 0010
1111 1001 0111 0001
…
WRITE TO
FSK_DEV_SPI_FAST
518
1357
1678
…
64178
63857
…
(1) Synthesizer mode, fVCO = 4800 MHz, fOUT = 480 MHz, fPD = 100 MHz, Prescaler = 2, DEN = 224, Use Equation 4 and Equation 6 to
calculate the step value.
In FSK I2S mode, clock in the desired binary format FSK steps in the FSK_D1 pin.
t0
t1
Figure 53. FSK I2S Mode Example
FSK_D1
FSK_DV
FSK_D0
To enable FSK I2S mode, set
FSK_MODE_SEL1 = 1
FSK_MODE_SEL0 = 0
FSK_EN_F1 =1
8.1.2 Frequency and Output Port Switching with TrCtl Pin
Register R0, RXTX_CTRL, and RXTX_POL are used to define the output port switching behavior with the TrCtl
pin. To enable switching with TrCtl pin, set RXTX_CTRL=1.
RXTX_CTRL
1
1
1
1
RXTX_POL
0
0
1
1
Table 35. TrCtl Pin Usage
TrCtl PIN
0
1
0
1
RFoutTx
Active
Active
RFoutRx
Active
Active
Register R0, F1F2_CTRL, and F1F2_SEL define the operation of the frequency switching between the two pre-
defined frequencies F1 and F2. To switch frequency using the TrCtl pin, set F1F2_CTRL to 1. F1F2_SEL selects
the output frequency for the current status. For example, if the current active output frequency is F1, toggling
TrCtl pin will change the output frequency to F2. Toggling TrCtl pin again will change the output frequency back
to F1.
8.1.3 OSCin Configuration
OSCin supports single-end clock, differential clock as well as crystal. Register R34 defines OSCin configuration.
36
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