DT2821 CONFIGURATION PARAMETERS:

• Parameter overview
• Address
• Channel preset, SE/DI setting
• DMA (Direct Memory Access) level
• Help File omit
• IRQ (Interrupt ReQuest)
• Model
• Output DAC range (reference only)
• Port I/O (DIO) configuration
• Input Range preset
  • x2 range jumpers
  • Bipolar / Unipolar ranges
  • ADC coding - Straight Binary, Offset, or 2s Complement
• Conversion Speeds, ADC and DAC
  • External Pacer preset

PARAMETER OVERVIEW:

    DT2821.ADC      A:h300  I:5  M:21FS

Daqarta does not use any SET lines in your AUTOEXEC.BAT file, nor does it use any non-Daqarta drivers or libraries that may have been supplied by Data Translation or others.

You can check to see which parameters have been set, either via the configuration line or by default, by checking the board information summary available via the ALT-H Plug-In Help system. This also shows a summary of the default values for all parameters. There is no need to enter any parameter that is the same as the default value assumed by Daqarta.

A: ADDRESS:

    DAS20.ADC      A:h300

    'DT2821-series board not found.'

The only exception is if you set A:0 to allow viewing of this board Help system without having a board installed or properly configured.

The DT2821-series uses jumpers W15 - W18 to set the base address. These jumpers form a binary-weighted value with each jumper IN counting for 0 and OUT counting as follows:

    W15 = 100h
    W16 =  80h
    W17 =  40h
    W18 =  20h

There is also an implied 200h that is always present. So the total possible address range is from 200h (all IN) to 3E0h (all OUT). The 240h factory default is:

             200h  =   200h (always)

 W15    IN   100h  =     0

 W16    IN    80h  =     0

 W17    OUT   40h  =    40h

 W18    IN    20h  =     0

               TOTAL:  240h = BASE ADDRESS

C: CHANNEL PRESET, SE/DI SETTING:

    DT2821.ADC      C:3

The range of allowable channel values depends upon the model (as set by the M: parameter) and on the position of the Single Ended / Differential Input jumpers W3 - W6, if applicable to that model. For the straight DT2821 the jumpers select between 16 SE channels 0-15 or 8 DI channels 0-7 (factory default).

The status of the jumpers is not directly readable via software, so you need to tell Daqarta which way they are set. If they are set to SE, use an S in front of the selected channel number, as in:

    DT2821.ADC      C:S3

This sets the same initial channel as the previous example, but allows the Channel control in the menu to range from 0-15 instead of the assumed DI factory default of only 0-7. Note that there is no effect upon the hardware itself.

You can use the C:Dn form to specify DI mode, even though DI is the assumed default. This can serve as a reminder to yourself or others in your lab, since there is no simple way to tell which way the jumpers are set from outside the system.

A model without selectable SE/DI modes will automatically be limited to the appropriate channel range for that model, as determined by the M: parameter.

If you use the C:Sn parameter on a model that only has differential inputs, Daqarta will exit with:

    'No SE capability on specified Model.'

    'No DI capability on specified Model.'

If you set a channel number that is too high for the SE/DI mode and model, Daqarta will exit with:

    'Specified channel exceeds DI limit on this Model.'

    'Specified channel exceeds SI limit on this Model.'

Once Daqarta is running, the ALT-H summary screen will show whether the mode is Single-Ended or Differential.

D: DMA (Direct Memory Access) Level:

The factory and Daqarta default is level 5. The setting can't be read directly from the board via software, so if you need to use another level, use a DQA.CFG line like:

    DT2821.ADC      D:6

Levels 5 or 6 can be set via simple jumper plugs, but level 7 requires wire jumpers:

             DMA REQUEST                DMA ACKNOWLEDGE

 DMA  o W19 o W20 o W21 o W22 o    o W23 o W24 o W25 o W26 o

  5   o-jmp-o     o     o     o    o-jmp-o     o     o     o

  6   o     o-jmp-o     o     o    o     o-jmp-o     o     o

  7   o     o     o     o     o    o     o     o     o     o
             \-----wire------/            \-----wire------/

F: HELP FILE OMIT:

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.

I: IRQ (Interrupt ReQuest):

  IRQ   Jumper

   7     W31

   5     W30

   3     W29

   15    W28    (Default)

   10    W27

    DT2821.ADC      I:5

For maximum performance with STIM3 outputs in RTime mode, you may want to avoid IRQs 10 and 15. These IRQs use the system's second interrupt controller, which requires an extra End Of Interrupt (EOI) command to acknowledge each interrupt. This takes a little more time and could reduce the maximum sample rate possible in interrupt-driven operation, which is only used when STIM3 outputs are active in RTime mode. The extra time will have no effect on normal DMA RTime (ADC only) or on Sequential mode (with or without STIM3 outputs).

If you use interrupt-driven RTime, you may need to use the special DDISK13 BIOS-replacement driver for DDisk recording. This will only work with drives of 528 Meg or less. For larger drives, you will need to conduct your own tests to see if you can get suitable glitch-free recordings at your chosen sample rate, etc.

M: MODEL:

    DT2821.ADC      M:DT2821-F-16SE

    DT2821.ADC      M:21FS

O: OUTPUT DAC RANGE (Reference Only):

 - Jumpers -    --------- RANGE, Volts ------------

 DAC1   DAC0   +/-10   +/-5   +/-2.5    0-10    0-5

 W11     W7      -       -      IN       -      IN

 W12     W8      -      IN      IN      IN      IN

 W13     W9     IN      IN      IN       -       -

 W14     W10    IN       -       -       -       -

             (Default)

    B10     Bipolar 10 Volts
    B5      Bipolar 5 Volts
    B2.5    Bipolar 2.5 Volts
    U10     Unipolar 10 Volts
    U5      Unipolar 5 Volts

    DT2821.ADC      O:B5

If you set the individual DACs differently, put the DAC number just after the colon. For instance, with DAC 0 set to +/- 5 and DAC 1 set to 0-10 Volts, use:

    DT2821.ADC      O:0B5  O:1U10

In general, you will probably want bipolar ranges for most work, since then the output will be 0 Volts when it is off. For unipolar ranges Daqarta will provide a half-scale offset so that sine waves swing between 0 at negative peaks and the maximum value (5 or 10 Volts) at positive peaks.

Note that values you set with the O: parameter are strictly for your own reference. Daqarta actually ignores the ranges you specify here, since they pertain only to the analog gain of the DAC outputs, not to the digital values Daqarta uses to control the waveforms. If you specify different ranges than have been set via the jumpers, the waveforms will still be correct even if their levels are not as shown on the summary screen.

P: PORT I/O (DIO) CONFIGURATION:

    DT2821.ADC      P:O1

The Board control menu allows selection of digital I/O bits for various functions. You will typically hard-wire these items once your system is set up, so it makes sense to preset these bit assignments at start-up. The P: parameter allows you to specify bit usage other than the defaults.

Use a letter after the P: to specify usage, followed by a digit (n) from 0 to 7 to specify the bit for that use. (Letters are not case-sensitive.)

  Parameter     ---- Usage ----         Default
    P:En        External Trigger    Dig In 0
    P:Dn        DDisk Remote        Dig In 1
    P:An        Averager Remote     Dig In 2
    P:Pn        Pulse Output        Dig Out 0

R: INPUT RANGE PRESET:

Most models allow the input range control to select one of 4 different input ranges. Depending on the model, these are from the standard PGH ranges or the low-level PGL ranges, as indicated in the Models and Features table.

    PGH:        PGL:
    10          10
    5.0         1.0
    2.5         0.1
    1.25        0.02

Models DT2821-G-16SE and DT2821-G-8DI use the PGH range series, but also allow jumper selection of an additional 2x gain applied to all ranges. Similarly, the DT24-EZ-PGL normally uses the PGL ranges, but these may also be doubled:

    PGHx2:      PGLx2:
    5.0         5.0
    2.5         0.5
    1.25        0.05
    0.625       0.01

Boards are set to the +/- 10 Volt range by default. If you want to set +/- 5 Volts instead, for example, you can use:

    DT2821.ADC      R:5

If you have a DT2821-G-16SE or -8DI model, Daqarta will assume the same thing. But if you have set the jumpers for the x2 configuration, there is no way for Daqarta to read that status directly from the board. You must tell Daqarta that this 5 Volts is the top range of an x2 series and not the second range of the standard series, by using:

    DT2821.ADC      R:X5

If Daqarta is not told about the x2 jumper, you will get the wrong range selection. This is only needed where there is ambiguity about the x2 jumper: If you give

    DT2821.ADC      R:0.625

Daqarta also assumes any range value you give is a bipolar range. If you have set the unipolar jumper configuration (which also can't be read directly from the board), then you must tell Daqarta via a U after the colon, as in:

    DT2821.ADC      R:U5

Note that the DT2821-G-16SE and -8DI models don't allow both x2 and unipolar jumpers. The DT24-EZ-PGL does allow both together, but only the 'U' is needed, not an 'X' as well, because as mentioned earlier Daqarta can always infer the relevant x2 setting from the range value.

In addition to the range preset and the presence of x2 or unipolar jumper settings, you also use the R: parameter to tell Daqarta about the data format used by the ADC. The default is Offset Binary, but Unipolar ("straight") Binary and Two's Complement are also selectable via jumpers W32-W39 on most models. (These are scattered all over the board; see your owner's manual.)

If you set the unipolar jumpers and use an R:Un parameter, Daqarta assumes straight binary coding has also been selected via W32-W39.

With bipolar ranges, most models allow Two's Complement coding instead of the default Offset Binary via these jumpers. There is no advantage to using this with Daqarta, but you may need it for compatibility with existing software. If you do this, add a 'T' before the range value, as in:

    DT2821.ADC      R:T10

If you have also selected x2 ranges, you can combine this with the 'X', as in:

    DT2821.ADC      R:UT5

Aside from the 'X', 'U', or 'T' letters, Daqarta tries to match any given range value with one of those in the following lists:

PGH models:      PGL models:
   10                10
   5                 5
   2.5               1
   1.25              0.5
   0.625             0.1
                     0.05
                     0.02
                     0.01

    'Invalid R: Range parameter.'

Certain R: parameter errors will cause Daqarta to exit with one of the following messages:

    'R:Xn given, but specified Range is not x2.'

    'Model does not support x2 Range jumper.'

    'Specified R: Range not available on this Model.'

    'Only 10V Range on this Model.'

S: CONVERSION SPEEDS, ADC and DAC:

To specify a different conversion speed, you must follow the S: parameter with a letter A for setting the ADC speed or a D for the DAC speed, followed by the minimum sample period in microseconds. For example,

    DT2821.ADC      S:A12  S:D5

The minimum value you can set is 2 microseconds (500 kHz), and the maximum is 100 microseconds (10 kHz).

To determine the maximum ADC sample rate, start with a small period like S:A2. Use a known-good input waveform from any convenient source, such as a benchtop oscillator or function generator, or another system running Daqarta with an active STIM3 DAC or sound card Synth output. The frequency is not critical (1 kHz or so is fine), nor is the exact waveform (but triangle or sine is probably best... not square wave).

With the ADC sample rate at the start-up default of 20 kHz, adjust the input level to get a clean display of your input signal that is around half of full-scale. Now go to the X-axis control menu and raise the sample rate until you see the waveform begin to visibly distort, typically becoming noisy and spiky. Check both Sequential and RTime modes, and decide on a safe upper limit. Read the sample period directly from the menu item, and save this to use as your S:A value.

To find the maximum DAC rate, again start with a small period like S:D2. Feed one of the DAC outputs back to the ADC input. Bring up the STIM3 menu (CTRL-G) and activate that DAC. In Sequential mode, go to the Factor item and slowly raise it until you see visible distortion on the ADC trace. Ideally, you might also want to check this on an external oscilloscope, if one is available. But the ADC trace will typically show distortion sooner than the DAC output (due to slow CPU or ISA bus problems), so the ADC trace will probably be the limiting factor anyway.

Go to the X-axis menu and read the sample period directly, then divide by the Factor to get the S:D value. (Daqarta allows the DACs to run faster than the maximum ADC limits by means of its unique "hypersampling" operation.)

Repeat the test with both DACs active... you may find poorer performance. Now repeat the single-DAC and dual-DAC tests in RTime mode and you will typically find even poorer performance, especially on slow systems.

In RTime mode if you adjust the sample rate to get the fastest setting that just eliminates problems, you may find that spikes still appear on each keystroke unless you slow the sample rate even more. You may want to avoid operating in this "twitchy" range for normal work, but it can be used if you are aware of the limitations and don't use any keystrokes during averaging or DDisk recording, for example.

Decide where to set the ADC and DAC limits, based upon your own needs. For example, if you will be the only user and will run mostly in Sequential mode where higher sample rates can be achieved, you can base your S: settings on those values. Or you may want to set more conservative values to "bullet-proof" the system for less-knowledgeable users.

EXTERNAL PACER PRESET:

A typical use would be:

    DT2821.ADC      S:E5

You can set any integer value from 2 to 65535 here. If your pacer signal is constant, or nearly so, you can just use the closest integer microsecond approximation of its period. If it varies all over the place, you may be better off with a 0 to 100% representation.

For analyzing rotating machinery, sample pulses are typically derived from a magnetic or optical pickup that monitors the passing teeth of a gear. If you want the X-axis to read directly in multiples of the main shaft speed (harmonic numbers), you need to do a little planning.

For example, suppose you put the pickup on a gear with 100 teeth, and that gear is driven 4 times faster than the main shaft. Then the pickup produces pulses 400x faster than the main shaft revolves. If you want the main shaft frequency (fundamental) to show as 1 Hz, you must indicate that the sample rate is 400 Hz (2500 microseconds) via S:E2500. The X-axis will then show 0 to 200 Hz, which you can interpret as 0 to the 200th harmonic.

Note that when you use the S:En option instead of the Pacer control, the sample period and frequency items in the X-axis menu will not be adjustable. If you use the Pacer control instead of S:En, you can change these items (and hence the frequency axis displayed), but either way the true sample rate is determined only by the external clock input on pin 50.

Additional discussion of external pacer operation is provided under the Pacer control topic.

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