UG-075
Evaluation Board User Guide
Rev. 0 | Page 8 of 16
PLL REFERENCE INPUT WINDOW
The
Reference Input Control
window is shown in Figure 10
and is accessed by clicking either of the triangular buffer symbols
immediately to the right of the
REF 1 (MHz)
and
REF 2 (MHz)
input reference frequency boxes (see Figure 9).
0
87
45
-00
6
Figure 9. Buffer Symbol
08
74
5-
0
07
Figure 10. Reference Input Control Window
This window is used to enable the PLL reference inputs, which
are powered down by default.
Select
Enable REF 1
, or
Enable REF 2
, or both to enable the
appropriate reference input, and click
OK
when finished. If a
differential input is used, select the
Use Differential Ref Mode
(Unchecked = Single-Ended Mode)
check box. Note that this
mode should not be used simultaneously with
Enable REF 1
or
Enable REF 2
.
The remaining four check boxes control the reference switch-
over modes. If
Disable Switchover De-Glitch
is activated, the
AD951x maintains the phase relationship between the active
input and PLL output during a reference switchover. Otherwise,
the AD951x minimizes the phase disturbance at the output
during a reference switchover.
PLL CONFIGURATION WINDOW
The
PLL Configuration
window shown in Figure 11 is opened
by clicking the
Config PLL
button on the main screen. This
window has three sections:
SyncB Counter Reset Mode
,
ReadBack Registers
, and
Settings
.
The
SyncB Counter Reset Mode
section indicates whether the
R, A, and B counters are reset when the SYNC pin is activated, and
controls R0x019[7:6]. See the AD951x data sheet for more
details.
The
ReadBack Registers
section allows you to see the current
value of the read-only PLL status register (Address 0x01F). This
function is very useful for ensuring that the AD951x VCO has
finished VCO calibration, and that the PLL is locked.
The
Settings
section controls the various PLL settings such as hold-
over. The AD951x data sheet describes these functions in detail.
Note that the automatic holdover feature should not be enabled
during VCO calibration.
08
74
5-
0
08
Figure 11. PLL Configuration Window
REFMON, STATUS, AND LD BUTTONS
These three blue buttons (
REFMON
,
STATUS
, and
LD
) allow
you to select which signals appear at the REFMON, STATUS,
and LD pins at Connector P1. Connector P1 is located in the
center of the evaluation board. The pins in the left column
of Connector P1 are ground pins, and the ones in the right
column are signal pins.
There are many useful diagnostic signals available at these
pins. The R divider output is particularly useful. In the example
used in the Quick Start Guide to the AD9516 PLL section, the
80 kHz signal is visible on the STATUS pin to ensure that the
reference inputs and R divider are working properly.
Dynamic signals (such as the R divider output) are primarily
intended for diagnostics. These diagnostic signals may adversely
affect PLL performance in critical applications if left on in
normal operation.
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