2.7 R4 REGISTER

This register is used to setup the N divider for the RF Synthesizer. A single word write to this register is all that is required to power

up and tune the RF synthesizer to the desired frequency.

Reg

23

22

21

20

19

18

17

16

15

14

13

12

11

10

9876543210

DATA[20:0]

C2

C1

C0

R4

RF_

PD

RF_N[12:0]

RF_FN[6:0]

1

0

0

2.7.1 RF_FN — Fractional Numerator, RF Synthesizer

In the case that the PLL is operating in fractional mode (RF_OM=1), RF_FN[6:0] specifies the fractional numerator of the

complete N counter value of the RF PLL. In the case that the PLL is operating in integer mode (RF_OM=0), RF_FN adds to the

total value of the N counter.

Operating Mode

RF N Divider Value Calculation

Fractional Mode (RF_OM=1)

RF_N +RF_FN/RF_FD

Integer Mode (RF_OM=0)

RF_N x RF_FD + RF_FN

2.7.2 RF_N[12:0] — N Divider Ratio, RF Synthesizer

RF_N[12:0] specifies an integer value that is used in calculating the N divider ratio for the RF synthesizer. In the case the part is

operating in fractional mode, it value is the N divider ratio. In the case the part is operating in integer mode, this number is used

in conjunction with the RF_FD and RF_FN values to calculate the N divider value. The range of values supported is dependant

on the selected prescaler. When the 8/9/12/13 prescaler is selected, RF_N value can range from 40 to 4095. When the

16/17/20/21 prescaler is selected, the RF_N value can range from 80 to 8191. The following tables describe how to program a

specific value of RF_N for a given prescaler.

The RF_N value is actually created using a prescaler, C counter, B counter, and an A counter. If RF_P = 16, then the RF_N[12:0]

word is just the binary representation of the desired value. If RF_P = 8, then the case is similiar, except that the third LSB is

disregarded in all calculations. The relationship between RF_N, RF_P, RF_A, RF_B, and RF_C is shown below.

RF_N = RF_PxRF_C +4xRF_B + RF_A

RF_N[12:0] Programming with RF_P = 16

RF_N[12:0]

12

11

10

987654

3

2

1

0

RF_C[8:0]

RF_B [1:0]

RF_A[1:0]

0–47

Values from 0–47 are not allowed.

Some of these N values are allowed, others are illegal divide ratios and not allowed.

48–79

Legal Divide Ratios in Fractional Mode:

48–49, 52–53, 64–66, 68–70, 72–74, 76–78

Legal Divide Ratios in Integer Mode:

All these values are legal in integer mode.

80

0

0

0

000101

0

0

0

0

81

0

0

0

000101

0

0

0

1

…

8191

1

1

1

111111

1

1

1

1

RF_N[12:0] Programming with RF_P = 8

RF_N[12:0]

12

11

10

987654

3

2

1

0

RF_C[8:0]

RF_B[1:0]

RF_A[1:0]

0–23

Values from 0–23 are not allowed.

Some of these N values are allowed, others are illegal divide ratios and not allowed.

24–39

Legal Divide Ratios in Fractional Mode:

24–25, 28–29, 32–34, 36–38

Legal Divide Ratios in Integer Mode:

All these values are legal in integer mode.

40

0

0

0

000011

X

0

0

0

41

0

0

0

000011

X

0

0

1

…

4095

1

1

1

111111

X

1

1

1

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