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參數(shù)資料
| 型號： | AD9547/PCBZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 27/104頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD EVALUATION FOR AD9547 |
| 設(shè)計資源： | AD9547 Schematic AD9574 BOM |
| 標(biāo)準(zhǔn)包裝： | 1 |
| 主要目的： | 計時，時鐘發(fā)生器 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | AD9547 |
| 主要屬性： | 2 個差分式或 4 個單端輸入 |
| 次要屬性： | CMOS，LVPECL 和 LVDS 兼容 |
| 已供物品： | 板 |
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Data Sheet
AD9547
Rev. E | Page 29 of 104
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 AssignmentState Machine
The functional flexibility of the AD9547 resides in the way that
it assigns aparticular 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
A
0
Profile # (or null)
AA
1
Profile # (or null)
B
2
Profile # (or null)
BB
3
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,
Register 0x0D0E for REF B, and Register 0x0D0F for REF BB. Bit 7
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
register (Address 0x0A0D). The state machine activates imme-
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 toRegister 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 areference 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 successfulreference period measurement by the validation
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.
As long as there are input references programmed for automatic
profile assignment, and for which the profile assignment is null,
the state machine continues to cycle through those references
searching for a profile match. Furthermore, unless an input
reference is assigned to a profile, it is considered invalid and
excluded as a candidate for a reference switchover.
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