AD9547SLASHPCBZ datasheet(29/104 Pages) AD

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AD9547

Rev. 0 | Page 29 of 104

Reference-to-Profile Assignment Control

The user can manually assign a reference to a profile or let the

device make the assignment automatically. The manual reference

profile selection register (Address 0x0503 and Address 0x0504)

is used to program whether a reference-to-profile assignment is

manual or automatic. The manual reference profile selection regi-

ster is a 2-byte register partitioned into four half bytes (or nibbles).

The four nibbles form a one-to-one correspondence with the four

reference inputs: one nibble for REF A, the next for REF AA, and

so on. For a reference configured as a differential input, however,

the device ignores the nibble associated with the two-letter input.

For example, if the B reference is differential, only the REF B nibble

matters (the device ignores the REF BB nibble).

The MSB of each nibble is the manual profile bit, whereas the

three LSBs of each nibble identify one of the eight profiles (0 to 7).

A Logic 1 for the manual profile bit assigns the associated ref-

erence to the profile identified by the three LSBs of the nibble.

A Logic 0 for the manual profile bit configures the associated

reference for automatic reference-to-profile assignment (the

three LSBs are ignored in this case). Note that references

configured for automatic reference-to-profile assignment

require activation (see the Reference-to-Profile Assignment

State Machine section).

Reference-to-Profile Assignment State Machine

The functional flexibility of the AD9547 resides in the way that

it assigns a particular input reference to one of the eight reference

profiles. The reference-to-profile assignment state machine effec-

tively builds a reference-to-profile table that maps the index of

each input reference to a profile (see Table 22).

Table 22. Reference-to-Profile Table

Reference Input

Reference Index

Profile

Profile # (or null)

Each entry in the profile column consists of a profile number

(0 to 7) or a null value. A null value appears when a reference-

to-profile assignment does not exist for a particular reference

input (following a reset, for example). The information in Table 22

appears in the register map (Register 0x0D0C to Register 0x0D0F)

so that the user has access to the reference-to-profile assignments

on a real-time basis. Register 0x0D0C contains the information for

REF A, Register 0x0D0D contains the information for REF AA,

of each register is the null indicator for that particular reference.

If Bit 7 = 0, the pro-file assignment for that particular reference is

null. If Bit 7 = 1, that particular reference is assigned to the profile

(0 to 7) identified by Bits[6:4]. Note that Bits[6:4] are meaning-

less unless Bit 7 = 1.

Following a reset, the reference-to-profile assignment state machine

is inactive to avoid improperly assigning a reference to a profile

before the system clock stabilizes. The state machine relies on

accurate information from the reference monitors, which, in turn,

rely on a stable system clock. Because the reference-to-profile

assignment state machine is inactive at power-up, the user must

initiate it manually by writing to the reference profile selection

diately, unless the system clock is not stabilized. In that case,

activation occurs upon expiration of the system clock stability

timer. Note that initialization of the state machine is on a per-

reference basis. That is, each reference input is associated with an

independent initialization control bit.

When initialized for processing a reference, the state machine

continuously monitors that reference until the occurrence of a

device reset. This is true even when the user programs a reference

for manual profile selection, in which case the state machine

associated with that particular reference operates with its activity

masked. The masked background activity allows for seamless

operation if the user subsequently reprograms the reference for

automatic profile selection.

Reference-to-Profile Assignment

When a reference is programmed for manual profile assignment

(see Register 0x0503 to Register 0x0504), the reference-to-profile

assignment state machine puts the programmed manual profile

number into the profile column of the reference-to-profile table

(see Table 22) in the row associated with the appropriate reference.

However, when the user programs a reference for automatic profile

assignment, the state machine must determine which profile to

assign to the reference, as explained in the following paragraphs.

If a null entry appears in the reference-to-profile table for a parti-

cular input reference, the validation logic for that reference enters

a period estimation mode. Note that a null entry is the default

state following a reset, but it also occurs when a reference redetect

timer expires. The period estimation mode enables the validation

logic to make a blind estimate of the period of the input reference

with a tolerance of 0.1%. The validation logic remains in the period

estimation mode until it successfully estimates the reference period.

Upon a successful reference period measurement by the vali-

dation logic, the state machine compares the measured period

to the nominal reference period programmed into each of the

eight profiles. The state machine assigns the reference to the

profile with the closest match to the measured period. If more

than one profile exactly matches the reference period, the state

machine chooses the profile with the lowest numeric index. For

example, if the reference period in both Profile 3 and Profile 5

matches the measured period, Profile 3 is given the assignment.

To safeguard against making a poor reference-to-profile assign-

ment, the state machine ensures that the measured reference period

is within 6.25% of the nominal reference period that appears in

the closest match profile. Otherwise, the state machine does not

make a profile assignment and leaves the null entry in the refer-

ence-to-profile table.

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