LMX2542LQ2121 NSC [National Semiconductor], LMX2542LQ2121 Datasheet - Page 16

• Manufacturer Part Number: LMX2542LQ2121
• Description: PLLatinum Cellular and GPS Frequency Synthesizer System with Integrated VCO
• Manufacturer: NSC [National Semiconductor]

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Reg
R0 SPI_
2.0 Programming Description
2.2 R0 REGISTER
The R0 register contains the RF_FN, RF_A, RF_B, RF_LD, and SPI_DEF control words. The register address bits are R0[1:0]
2.2.1 RF_FN[10:0] - RF Synthesizer Fractional Numerator Counter (R0[2:12])
The RF_FN control word is used to setup the 11-bit ∆Σ modulator. This corresponds to programming the fractional numerator
counter portion of the RF feedback divider. The value programmed is dependent on the reference oscillator used.
2.2.1.1 Programming RF_FN[10:0] Using 19.20 MHz Reference Oscillator
When a 19.20 MHz reference oscillator is used (OSC_FREQ bit = 0), the RF_FN can be programmed to values ranging from 0
to 1919.
2.2.1.2 Programming RF_FN[10:0] Using 19.68 MHz Reference Oscillator
Similarly, when a 19.68 MHz reference oscillator is used (OSC_FREQ bit = 1), the RF_FN can be programmed to values ranging
from 0 to 1967.
2.2.2 RF_A[2:0] - RF Synthesizer Swallow Counter (A Counter) (R0[13:15])
The RF_A control word is used to setup the RF synthesizer’s A counter. The A counter is a 3-bit swallow counter used in the
programmable feedback divider. The RF_A control word can be programmed to values ranging from 0 to 7.
= 00. The detailed descriptions and programming information for each control word is discussed in the following sections.
MSB
DEF
23
Divide Ratio
22
1
RF_
LD
21
0
1
7
•
Numerator
Numerator
20
0
1919
1967
0
1
0
1
•
•
19
18
RF_B
[3:0]
17
16
10
10
0
0
1
0
0
1
•
•
2
0
0
1
•
15
9
0
0
1
9
0
0
1
•
•
RF_A
[2:0]
SHIFT REGISTER BIT LOCATION
14
(Continued)
DATA[21:0] FIELD
8
0
0
1
8
0
0
1
•
•
13
12
16
7
0
0
0
7
0
0
1
•
•
f
11
f
OSCin
OSCin
6
0
0
0
6
0
0
1
•
•
RF_FN[10:0]
RF_FN[10:0]
10
RF_A[2:0]
RF Mode
= 19.68 MHz
= 19.20 MHz
5
0
0
1
5
0
0
1
•
•
1
0
0
1
•
9
4
0
0
1
4
0
0
0
8
•
•
RF_FN
[10:0]
7
3
0
0
1
3
0
0
1
•
•
6
2
0
0
1
2
0
0
1
•
•
5
1
0
0
1
1
0
0
1
•
•
4
0
0
1
1
•
3
0
0
1
1
0
0
1
1
•
•
2
ADDRESS
1
0
FIELD
[1:0]
LSB
0
0