AD9520-1SLASHPCBZ datasheet(70/80 Pages) AD

70 / 80 page

AD9520-1

Data Sheet

Rev. B | Page 70 of 80

Reg.

Addr.

(Hex)

Bits

Name

Description

0x01D 7

Enable

STATUS_EEPRO

M at STATUS pin

Enables the STATUS_EEPROM signal at the STATUS pin.

0: the STATUS pin is controlled by the Register 0x017[7:2] selection.

1: selects the STATUS_EEPROM signal at the STATUS pin. This bit overrides the Register 0x017[7:2] selection (default).

Enable XTAL OSC Enables the maintaining amplifier needed by a crystal oscillator at the PLL reference input.

0: crystal oscillator maintaining amplifier disabled (default).

1: crystal oscillator maintaining amplifier enabled.

Enable clock

doubler

Enables PLL reference input clock doubler.

0: doubler disabled (default).

1: doubler enabled.

Disable PLL

status register

Disables the PLL status register readback.

0: PLL status register enabled (default).

1: PLL status register disabled. If this bit is set, Register 0x01F is not automatically updated.

Enable LD pin

comparator

Enables the LD pin voltage comparator. Used with the LD pin current source lock detect mode. When the AD9520-1 is in internal

(automatic) holdover mode, this bit enables the use of the voltage on the LD pin to determine if the PLL was previously in a locked

state (see Figure 47). Otherwise, this can be used with the REFMON and STATUS pins to monitor the voltage on the LD pin.

0: disables LD pin comparator and ignores the LD pin voltage; the automatic/internal holdover controller treats this pin as true

(high, default).

1: enables the LD pin comparator (uses the LD pin voltage to determine if the PLL was previously locked).

Unused

Unused.

Enable external

holdover

Enables the external hold control through the SYNC pin. (This bit disables the internal holdover mode.)

0: automatic holdover mode; holdover controlled by the automatic holdover circuit (default).

1: external holdover mode; holdover controlled by the SYNC pin.

Enable holdover Enables the internally controlled holdover function.

0: holdover disabled (default).

1: holdover enabled.

0x01E

[7:5]

Unused

Unused.

[4:3]

External zero

delay feedback

channel divider

select

Bit

Selection of Channel Divider for Use in the External Zero-Delay Path

Selects Channel Divider 0 (default).

Selects Channel Divider 1.

Selects Channel Divider 2.

Selects Channel Divider 3

Enable external

zero delay

Selects which zero delay mode to use.

0: enables internal zero delay mode if Register 0x01E[1] = 1 (default).

1: enables external zero delay mode if Register 0x01E[1] = 1.

Enable zero

delay

Enables zero delay function.

0: disables zero delay function (default).

1: enables zero delay function.

Unused

Unused.

0x01F

Unused

Unused.

VCO calibration

finished

(read only)

Readback register. Indicates the status of the VCO calibration.

0: VCO calibration not finished.

1: VCO calibration finished.

Holdover active

(read only)

Readback register. Indicates if the part is in the holdover state (see Figure 47). Note that this is not the same as holdover enabled.

0: not in holdover state.

1: holdover state active.

REF2 selected

(read only)

Readback register. Indicates which PLL reference is selected as the input to the PLL.

0: REF1 selected (or differential reference if in differential mode).

1: REF2 selected.

VCO frequency >

threshold

(read only)

Readback register. Indicates if the VCO frequency is greater than the threshold (see Table 17, REF1, REF2, and VCO frequency

status monitor parameter).

0: VCO frequency is less than the threshold.

1: VCO frequency is greater than the threshold.

REF2 frequency >

threshold

(read only)

Readback register. Indicates if the frequency of the signal at REF2 is greater than the threshold frequency set by Register 0x01A[6].

0: REF2 frequency is less than the threshold frequency.

1: REF2 frequency is greater than the threshold frequency.

REF1 frequency >

threshold

(read only)

Readback register. Indicates if the frequency of the signal at REF1 is greater than the threshold frequency set by Register 0x01A[6].

0: REF1 frequency is less than the threshold frequency.

1: REF1 frequency is greater than the threshold frequency.

Digital lock

detect

(read only)

Readback register. Digital lock detect.

0: PLL is not locked.

1: PLL is locked.

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