Basic use ========= When the program runs, it checks to see whether an MMB0 is connected. If it is, it downloads the firmware to it, and runs; otherwise, it shows a dialog box telling you that it cannot find an MMB0. If you see this, make sure the MMB0 is connected and powered on, correct this if necessary, and click "Retry". If you cannot fix the problem, click "Cancel" to quit. After the program loads the MMB0 successfully, you will see a screen similar to that shown in Figure !!!. The top display shows an FFT of the ADC's output up to the Nyquist frequency (half the sampling rate), and certain AC analysis numbers. Below this are a number of controls and meters, and at the bottom is a set of tabs, which show either a histogram, a picture of the incoming waveform, or the data recording controls. To exit the program, select "File -> Exit" from the menu bar. When the program starts, it is idle. You can put it in either Acquire mode or Record mode. Acquire mode ============ To put the program into Acquire mode, click the "Acquire" button. In Acquire mode, the ADS1271EVM software collects data as quickly as possible from the board in 2,048-sample blocks and analyses it. Both AC and DC analyses are performed. In Acquire mode, you can only view the data from one channel at a time. To choose channels, use the Channel box. AC analysis consists of the FFT display and THD analysis. For THD analysis to work, the input must be a sine wave below half the Nyquist frequency, since the THD analyzer needs at least one harmonic to work from. The THD analyzer uses an automatic tone-detection algorithm, which searches for the highest harmonic and uses that for THD analysis. The frequency it detects is shown in the indicator marked "Tone Freq.". This frequency may not be exactly what your oscillator is set for, but it should generally be very close. For DC analysis, the program provides DC RMS noise (standard deviation), peak amplitude, and a DC level meter. A histogram is also provided; this is visible in the left tab. Basic DC measurements work best when the ADC is driven by an amplifier or stable voltage source; shorting the inputs also works. Data recording ============== To record data, go to the Record To File tab and do the following: - If Acquire is on, turn it off. You cannot start recording when Acquire is on. - Set the Conversion Mode and Sample Rate fields to the settings you want to record with. The channel selector has no effect for data recording. - Enter a path in the "Destination File" field. You can use the folder icon to browse for the file with a standard file dialog. If the file you enter cannot be opened or created, the record button will be disabled. If the path points to an existing file, the file will be overwritten when you activate recording. - Enter a number of samples to convert. You can enter this in time or number of samples; the other box will update automatically. The number of samples is limited by available memory on the MMB0. - Click the record button. You will see the "Samples Retrieved" bar graph increase. When it reaches the number of samples you selected, recording will stop and the record button will go dark. After this, the file you selected will contain comma-separated decimal numbers collected from the ADCs. The samples are written two to a line, with the sample from Channel 1 first, followed by a comma, followed by the sample from Channel 2. This kind of file can easily be imported into a spreadsheet, among other applications. Configuration ============= You can set the sample rate and conversion mode. Sample rate and conversion mode are always the same for each ADS1271 being evaluated; you cannot set one channel to a different parameter. The ADS1271's three conversion modes are selected from the flip-menu labelled "Conversion Mode". The ADS1271's clock is normally generated by a PLL synthesizer on the MMB0. The synthesizer cannot synthesize all frequencies precisely. The software will come as close as it can, but in some cases the sample rate will be slightly off. When you change the sample rate, you may find the value clamped or altered. The limits are different for high-speed mode: in that mode, the maximum sampling rate is approximately 105ksps, but in the other modes, it is approximately 52.5ksps. If you have the sampling rate set too high for another mode when you switch in to it, the program will automatically reduce the rate to the maximum for that mode. Note that the block size does not change. When you reduce the sampling rate, waveforms will appear to go up in frequency.