AD9546SLASHPCBZ datasheet(148/205 Pages) AD

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AD9546

Data Sheet

Rev. 0 | Page 148 of 205

Manual Translation Profile Selection with Fallback to

Priority-Based Translation Profile Selection

In the manual translation profile selection with fallback to

priority-based translation profile selection mode (Bits[3:2] = 1

decimal), the user specifies a particular translation profile for

manual operation in the same manner as described in the

Manual Translation Profile Selection with Fallback to Holdover

section. However, if the selected profile is not valid, rather than

switching to holdover mode, the DPLL attempts to use the

priority-based selection process (see the Automatic, Priority-

Based Translation Profile Selection section for a description of

priority-based selection). If the DPLL is unable to find a

translation profile per the priority selection process, the DPLL

switches to holdover or freerun operation per Figure 103.

Automatic, Priority-Based Translation Profile Selection

The priority associated with a particular translation profile

depends on the programmed value of Bits[5:1] of the following

and 0x12A0 for DPLL0 and 0x1600, 0x1620, 0x1640, 0x1660,

0x1680, and 0x16A0 for DPLL1. A lower value of Bits[5:1]

means a higher priority of the associated input reference

source. That is, 31 is the lowest (least favored) selection

priority, and 0 is the highest (most favored) selection priority.

In the automatic, priority-based translation profile selection

mode (Bits[3:2] = 0 decimal), the DPLL relies solely on the

automatic priority selection process shown in Figure 105 for

choosing a translation profile. However, if the DPLL is unable

to find a translation profile per the priority selection process,

the DPLL switches to holdover or freerun operation per

Figure 103.

As shown in Figure 105, the DPLL selects the most favored

translation profile when the current profile becomes invalid.

Translation Profile Validation

As shown in Figure 102, the manual and automatic translation

profile selection modes require validation of the selected

translation profile. Figure 104 shows a flowchart of the

translation profile validation process.

Part of the translation profile validation process requires

verification of the validity of the reference source associated

with the translation profile. Because the reference source

associated with a translation profile can be any of the following

five different source types (per Table 75), determining what

constitutes a valid reference depends on the source type:

•

REFA, REFAA, REFB, or REFBB reference input

•

Auxiliary REF0, auxiliary REF1, auxiliary REF2, or

Auxiliary REF3

•

IUTS0 or IUTS1

•

Auxiliary NCO 0 or NCO 1

•

DPLL0/DPLL1 feedback path

Figure 104 shows the source dependent validation decisions in

the reference source validation portion of the flowchart.

Revertive and Nonrevertive Reference Switching

Revertive reference switching means that if the reference

associated with a translation profile (Translation Profile 0, for

example) becomes invalid and the DPLL switches to a new

translation profile (Translation Profile 1, for example), and the

reference associated with Translation Profile 0 becomes valid

again, the DPLL switches back (reverts) to Translation Profile 0,

even though the reference associated with Translation Profile 1

is valid.

Nonrevertive reference switching means that if the reference

associated with a translation profile (Translation Profile 0.0, for

example) becomes invalid and the DPLL switches to a new

translation profile (Translation Profile 0.1, for example), the

DPLL continues to use Translation Profile 0.1 even if the

reference associated with Translation Profile 0.0 becomes valid

again. See the Automatic, Priority-Based Translation Profile

Selection section on how to assign a priority value to a

translation profile.

The automatic, priority-based translation profile selection

process provides for revertive and nonrevertive reference

switching using the difference between the priority of the

current translation profile and the priority of the previous

switched from translation profile to make the revertive or

nonrevertive decision. Specifically, if the priority value of the

current translation profile is at least 8 more than the priority

value of the switched from translation profile, the current

translation profile has significantly lower priority than the

switched from translation profile. Therefore, the DPLL reverts

to the switched from translation profile as soon as its reference

source becomes valid. Alternatively, if the priority value of the

current translation profile is 0 to 7 more than the priority value

of the switched from translation profile, the current translation

profile has only marginally lower priority than the switched

from translation profile. Therefore, the DPLL does not revert,

but remains with the current translation profile until its

reference source becomes invalid (or the user selects a new

translation profile manually).

In summary, the priority separation between the current

translation profile and the previously switched from translation

profile determines whether reference switching is revertive or

nonrevertive. Specifically, revertive switching requires the

priority value of the switched from translation profile to be at

least 8 lower than the priority value of the current translation

profile. Otherwise, nonrevertive reference switching applies.

That is, a priority separation of 8 marks the boundary between

revertive and nonrevertive reference switching.

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