Datasheet

UG-256 Evaluation Board User Guide
Rev. A | Page 6 of 20
MAIN WINDOW
The main window is divided into three tabs: Configure,
Program Voltage, and Measure DAC Output.
Configure
The Configure section allows access to the control register,
clearcode register, software control register, and DAC register
and also allows control of the
RESET
,
CLR
, and
LDAC
pins.
Program Voltage
The Program Voltage section programs the DAC register with
a value calculated from the entered values: the positive voltage
reference (VREFP), the negative voltage reference (VREFN),
and the desired output voltage (see Figure 4).
09762-004
Figure 4. Program Voltage Window
Measure DAC Output
The Measure DAC Output section allows the PC to control an
Agilent 3458A multimeter to measure and log the DAC output
voltage.
The multimeter is controlled over a general-purpose interface
bus (GPIB). Once connected to the PC, first configure the
multimeter via its front panel before taking a measurement.
Figure 6 shows the measurement options. The software runs
through a sequence of steps, programming the DAC register
and measuring the DAC output voltage. The sequence begins
with the software programming the DAC with the Start Code
value, incrementing the programmed value at each step by the
Code Step value, and finishing when the programmed value
reaches the Stop Code value. A delay between measurements
can be inserted, if required. The GPIB address of the multimeter
must be specified.
To begin the measurement, click START. The measurement can
be halted at any time by clicking STOP. When the measurement
is completed, a dialog box appears to allow the data to be saved
as a spreadsheet file with three columns of data. The first column is
the DAC code, the second column is the DAC voltage in volts,
and the third column is the INL error in LSBs, as shown in
Figure 5. A graph of both the DAC output voltage vs. the DAC
code and the INL error vs. the DAC code is displayed on-screen
(see Figure 6). In the measurement example shown in Figure 6,
measurements are taken in 1024 code steps beginning at Code 0
and finishing at Code 262,143 in total 256 measurements. With
the number of power line cycles (NPLC) setting on the multimeter
set to 1, the measurement takes ~18 sec to complete. To complete
an all codes measurement requiring 262,144 measurement
points takes ~6 hours to complete.
09726-005
Figure 5. Saved Data Format
If an Agilent 3458A multimeter is not connected to the PC,
the software steps through the codes without taking any
measurements.