Although the EVM GUI does not allow direct access to the levels and timing configuration of the ADC digital interface, the EVM GUI does give users high-level control over virtually all functions of the ADS8681W, including interface modes, sampling rate, and number of samples captured.

The various functions of the ADS8681W are exercised through the input parameters of the GUI (as well as the default values), as illustrated in Figure 4-3. These are global settings because the settings persist across the GUI tools listed in the top left pane as Pages, which include Register Map Configuration, Time Domain Display, Spectral Analysis, Histogram Analysis, and Linearity Analysis tools.

Figure 4-3 EVM GUI Global Input Parameters

The host configuration options in this pane allow the choice of various SPI and multiSPI host interface options available on the ADS8681W. The host always communicates with the ADS8681W using the standard SPI protocol over the single SDI lane, irrespective of the mode selected for Data Capture.

The drop-down boxes under the Device Modes sub-menu allows selection of the data capture mode. The Bus Width drop-down allows selection between Single-, and Dual-SDO lanes; Data Read between Source and System Synchronous modes; Device Range between Bipolar and Unipolar modes, and Voltage Range between 3 × Vref, 2.5 × Vref, 1.5 × Vref, 1.25 × Vref, and 0.625 × Vref options. Detailed descriptions of each of these modes are available in the ADS868x 16-Bit, High-Speed, Single-Supply, SAR ADC DAQ System With Programmable, Bipolar Input Ranges data sheet.

Selection of SCLK Frequency and Sampling Rate is allowed on this pane and is dependent of the Device Modes selected. Select or specify a target SCLK frequency (in Hz) and the GUI tries to match this as closely as possible by changing the PHI PLL settings and the achievable frequency that can differ from the target value displayed. Similarly, the sampling rate of the ADC can be adjusted by modifying the Target Sampling Rate argument (also in Hz). The achievable ADC sampling rate can differ from the target value, depending on the applied SCLK frequency and selected Device Mode and the closest match achievable is displayed. This pane allows the choice of various settings available on the ADS8681W in an iterative fashion until the best settings for the corresponding test scenario are discovered.

The final option in this pane is the selection for the Update Mode. The default value is Immediate, which indicates that the interface settings selection is applied to configure both the host and the ADS8681W instantly. The Manual option indicates that the selection is made only when the final choices are decided upon and the user is ready to configure the device. This is described in more detail in the following section.

The GUI is switched between hardware mode and simulation mode by checking and unchecking the Connected to Hardware box in the top right area at any time.