AD9956/PCB

Rev. 0 | Page 5 of 12

CONTROL DIALOG BOX

Use the Control dialog box to enable and disable individual

device functions, program the input clock speed, and toggle

various other options. Figure 3 shows the sections of the

Control

dialog box: Clock, Output Waveform, Linear Sweep,

Power Down

, Accumulator Control, and Sync Multi DUT’s.

Click Charge Pump/Clock Driver Window, I/O Interface

Window,

or DUT Signals Window to access these dialog

boxes.

LOAD and READ

At the bottom right of the dialog box are the LOAD and READ

buttons.

After you have made changes to the evaluation software, click

LOAD

to send the data to the device. In addition to sending

data, you can also configure LOAD to automatically send an

I/O update signal to the DUT when the software finishes

sending data. See the DUT Signals Dialog Box section for

details. When new data is ready to be sent, LOAD flashes

green, indicating that a you need to issue a LOAD.

Click READ to perform a readback of the currently program-

med status of the device and to update the GUI with the current

settings.

Figure 3. Control Dialog Box

Clock

To program the reference clock and the RF prescalar values:

1.

In the Ref Clock box, type the operating frequency of the

external reference clock. The maximum is 2.7 GHz.

2.

In the Divider Ratio box, select a divider value for the RF

prescalar. The value must be in the range of 1 and 8.

3.

Click LOAD.

To bypass the RF divider and pipe the REFCLK input directly to

the DDS core, select RF Divider RefClk Mux. Even though the

divider operates at /1, /2, /4, or /8, and this divided signal can be

ported to the PECL driver, the raw, undivided REFCLK is used

as the internal system clock when this box is checked. Do not

select this box, if the REFCLK input is greater than 400 MHz.

Output Waveform

In the Output Waveform box, select either a cosine(x) or a

sine(x) function for the angle-to-amplitude conversion.

Linear Sweep

Use the Linear Sweep section to enable the linear sweep

functions of the DDS. See the AD9956 data sheet for a detailed

explanation of these modes of operation.

Select Enable to turn on the frequency accumulator. If the No

Dwell

box is not checked, the part is set in ordinary linear

sweep mode.

Select both Enable and No Dwell to put the part into linear

sweep no-dwell mode.

When you select Load SRR @ I/O Update, the current

countdown of the sweep ramp rate is cleared every time an

I/O_UPDATE signal is sent to the part. When using manual

programming through the GUI, it is almost impossible to notice

the effect of this function because the sweep ramp rates cycle

through their countdown timers in less than 655 µs, even when

programmed to a maximum value.

The linear sweep parameters (delta frequencies and ramp rates)

are controlled in the Linear Sweep section (see Figure 3). The

sweep itself, however, is controlled by the Ramp Up and Ramp

Down

buttons, which appear at the bottom of the Profile dialog

box when the Linear Sweep Enable box is checked. See the

Profile Dialog Box section for details.

Power Down

In the Power Down section, select the check boxes for the

circuit blocks that you want to power down.

Accumulator Control

This section controls the clear functions for the phase and

frequency accumulators.

Select Auto Clear Frequency Accum. or Auto Clear Phase

Accum.

to clear and release the corresponding accumulator.

The auto clear function sets the accumulator to a known value

of 0 and then begins accumulating.