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Daqarta for DOS
Data AcQuisition And Real-Time Analysis
Shareware for Legacy Systems

From the Daqarta for DOS Help system:



The DEMO.ADC driver allows you to try most of Daqarta's features without installing a "real" ADC board. Instead of a true ADC which takes samples of an analog input signal, this driver takes samples of a system counter's current value.

Since the counter is a separate hardware device, its operation is independent from the sampling operation. This means that if the sampling operation is delayed for any reason, the counter will go on counting nonetheless. When the counter is finally sampled it will be the wrong value for the intended sample time, and will show up as a discontinuity in the waveform.

This intolerance for sampling errors allows DEMO to test the integrity of interrupt-driven DDisk recording: If sample interrupts are missed while data is being written to disk, errors will show up. That wouldn't happen if the samples were simply generated by software, as they are for the built-in Virtual Source: After a lapse of any duration, the software would simply continue where it left off, without acknowledging any missing time.

Another feature of this DEMO driver is that it allows you to record data in any standard format with 8, 12, or 16 bits. This allows you to emulate any real board for purposes of testing DDisk file compatibility with other software.

Also, DEMO allows you to use the STIM3 Stimulus Generator to provide a signal input instead of the system counter, just as though you had a real board with a DAC or digital output connected back to an ADC input. You can thus experiment with different stimulus parameters and view the resultant spectra.

And although this doesn't provide an integrity check like the counter does, it does allow DDisk recording of the stimulus for playback on another system as a conventional .WAV file. There is no added noise or distortion such as might arise from actually generating the stimulus with a DAC and recording it with another ADC.


Most ADC board drivers allow you to specify certain parameters on the second line of the DQA.CFG file. Each parameter is given as a letter and colon, followed immediately by a value.

However, since this DEMO driver was designed to work with all systems, without the need for any added boards, it doesn't require such things as base address, board model, or IRQ and DMA numbers that are normally set via parameters.

Thus, the only supported parameter is F:0 to suppress loading of this DEMO.HLP file. The DEMO.ADC driver normally attempts to load this file on start-up, and exits with an error message if it can't find it. Setting F:0 on the ADC configuration line tells the driver not to look for the file. You would probably only want to use this option if you are really short of DOS memory, since loading the Help file only increases memory use by a few hundred bytes for its separate link stack and directory. (The file itself shares the text buffer of the Main Help file.)

Note that ALL Help files, including main, can be omitted via an F:0 parameter on the INIT line (first line) of the DQA.CFG file. If this is present, no individual module Help will be loaded.


When used without the STIM3 Stimulus Generator active, this just changes the displayed channel number and nothing else. Channels from 0 to 15 may be set directly, with a start-up default of channel 0.

When STIM3 is used, certain channels behave as though they were wired to certain "board" outputs controlled by STIM3:

 Source          Stimulus
 CH0             DAC 0
 CH1             DAC 1
 CH2 -  CH7      Normal DEMO Waveform
 CH8             DOUT bit 0
 CH9             DOUT bit 1
 CH10            DOUT bit 2
 CH11            DOUT bit 3
 CH12            DOUT bit 4
 CH13            DOUT bit 5
 CH14            DOUT bit 6
 CH15            DOUT bit 7


This allows you to scroll among arbitrary input ranges of +/-10 V, 1 V, or 100 mV full scale. The size of the waveform on the trace remains unchanged, while only the Y-axis changes to show the new range.

The KeyOn option forces Range to +/-10 V, which is the default on start-up.


DEMO allows you to record its "input signal" as though acquired from a board with 8, 12, or 16 bits resolution. This format will be preserved in DDisk recordings and also reported in the Trace Bits item of the Trace Information Menu.

You can scroll to separate LO 12 and HI 12 settings, since a 12-bit value is acquired as a 16-bit word that is justified to either the upper or lower bits, as in conventional laboratory ADC boards:

     8:                xxxx xxxx
 LO 12:      0000 xxxx xxxx xxxx
 HI 12:      xxxx xxxx xxxx 0000
    16:      xxxx xxxx xxxx xxxx
The KeyOn option forces Bits to 16, which is also the default on start-up.


This toggles between 'Offset' for Offset Binary and '2s Cmp' for Two's Complement, which are the two binary data formats in standard use.

The KeyOn option forces Two's Complement, which is the default on start-up.


This controls the apparent frequency of the input signal to the DEMO "board". The signal is actually derived from reading a system counter at the sample rate, and this Frequency setting controls the count range... not, as you might expect, the rate of counting. (The count rate is fixed in all PC-type systems at 1.19318 MHz for bad historical reasons.)

Thus, with Frequency set to 100 Hz (the default), the counter is set to count 11932 "ticks" of this counter clock before reloading and repeating the count sequence. Daqarta reads the current count at each sample period, and converts it to a selected waveform with the proper number of data bits and format.

If the Frequency is set to a higher value, the counter will be set to count fewer ticks before repeating. Note that if the Ramp-F and Tri-F waveforms are selected, the height of the wave is directly related to the count value: At higher frequencies, the smaller counts result in smaller waveform amplitudes. (The other waveforms are scaled to give constant amplitude.)

The Frequency setting has no effect if the Stimulus Generator is active and the DEMO Source channel is set to show its output instead of the counter ramp.


This option allows you to scroll between several different waveforms:
 Ramp-F      Fast Ramp, level decreases with Freq
 Tri-F       Fast Triangle, level decreases with Freq
 Square      Fast Square, constant level
 Ramp        Ramp, constant level
 Tri         Triangle, constant level
 Sine        Sine, constant level
The Ramp-F, Tri-F, and Square waveforms are computed directly from the system timer count by simple means, so they are faster and thus may be more suitable when you are running at high sample rates in RTime mode on a slow system. The Ramp-F and Tri-F levels go down as frequency increases, whereas the Square level is constant.

The remaining Ramp, Tri, and Sine waveforms are all scaled from the system timer count to maintain a constant level, equal to half of the full scale range. They run a bit slower, possibly limiting the maximum RTime sample rate on slow systems.

The Sine mode is particularly useful for checking the DDisk capabilities of systems that will be using interrupt-driven RTime sampling, either for LPTX or laboratory-type ADC boards. If excessive lags associated with disk writes cause sample interrupts to be delayed, the signal timer counts will be wrong and the sine wave will be distorted. (Sound cards and some lab-type boards use DMA to avoid these problems.)

Using this DEMO driver you can check the system before installing (or building) the "real" ADC hardware. Since the time to generate a data point with DEMO is at least as long as the time to read a data point on most real ADC boards, this is a conservative test. It will show up differences between disk cache On and Off, or the presence of the DDISK13 driver, or the use of a RAM drive. You can use the automatic glitch scan method to check the DDisk files you record.


(Note: Versions are numbered according to the Daqarta version they were released with.)

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