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AD9545

Data Sheet

Rev. A | Page 106 of 157

selection process, it switches to holdover or freerun operation

per Figure 84.

As shown in Figure 86, priority-based selection involves an

automatic search through the Profile x.y selection priority bit

fields in Bits[D5:D1] of register addresses: 0x1200, 0x1220,

0x1240, 0x1260, 0x1280, 0x12A0, 0x1600, 0x1620, 0x1640,

0x1660, 0x1680, and 0x16A0. The goal is to identify the

translation profile with the most favored (lowest) Profile x.y

selection priority bit field value for a given channel (DPLL0 or

DPLL1). Thus, the DPLL selects the most favored translation

profile when the current profile becomes invalid.

Translation Profile Validation

As shown in Figure 83, the manual/automatic translation profile

selection modes require validation of the selected translation

profile. Figure 85 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 one of the three

different source types listed below (per Table 38), determining

what constitutes a valid reference depends on the source type.

•

REFA, REFAA, REFB, or REFBB reference input

•

Auxiliary NCO 0 or NCO 1

•

DPLL0/DPLL1 feedback path

The source dependent validation decisions appear in the

reference source validation portion of the flowchart shown in

Figure 85.

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 become 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 value of the Profile x.y

selection priority bit field of the current translation profile is at

least 8 more than the Profile x.y selection priority bit field of the

switched from translation profile, it means that 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 Profile x.y selection

priority bit field of the current translation profile is 0 to 7 more

than the Profile x.y selection priority bit field 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 value

of the Profile x.y selection priority bit field of the switched from

translation profile to be at least 8 lower than the Profile x.y

selection priority bit field of the current translation profile.

Otherwise, non-revertive reference switching applies. That is, a

priority separation of 8 marks the boundary between revertive

and nonrevertive reference switching.

Active Profile

When the DPLL selects a particular translation profile, whether

manually or automatically, the selected profile becomes active.

When a translation profile is active, the corresponding DPLLx

Profile y active bit is Logic 1, with Logic 0 constituting inactive.

The DPLLx Profile y active bits (where x is 0 or 1 and y is the 0

to 5) reside in Bits[D5:D0] of Register 0x3009 and Register 0x300A.

The IRQ status section of the register map indicates Logic 0 to

Logic 1 transitions of the DPLLx Profile y active bits via their

corresponding DPLLx Profile y activated bits in Bits[D5:D0] of

Registers 0x3013 and 0x3018. Because these are latched bits, the

user must clear them via Bits[D5:D0] of Register 0x200E and

Logic 1 transitions of the DPLLx Profile y active bits (see the

Interrupt Request (IRQ) section).

An active translation profile is not the same as a valid translation

profile. That is, a profile can be valid without being active.

When all translation profiles for a particular DPLL are inactive,

the user can find the most recently active profile via the 3-bit

DPLLx active profile bit field (where x is 0 or 1) in Bits[D6:D4]

of Register 0x3101 and Register 0x3201. The value of the 3-bit

number corresponds to the most recently active profile. If a

translation profile is currently active (as indicated by one of the

DPLLx Profile y active bits), the DPLLx active profile bit field

reflects the value of the currently active profile.

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