Daqarta for DOS Contents
External Trigger pulse to start each sweep in Sequential mode. Only the Busy input (Status port bit 7, or pin 11 on the DB25 connector) is used for this. That input is never used for anything else with the DigOut or DAC models, but may optionally be used as the ADC data input with SAR or MUX models by specifying C:4 for the Channel parameter on the LPTX.ADC line of the DQA.CFG file. In that case, no External Trigger option will be available.
The External Trigger input is ignored unless you select Extern as the Trigger Source. The trigger must be a TTL level transition, and may be either low-to-high or high-to-low to start the sweep, depending on how you set the Trigger Slope. A trigger pulse must be at least as long as one sample period to assure that it is detected, and may be of any longer duration. You can also set Slope to Alt in order to trigger on alternating transitions for special applications.
Waveform averaging with the external trigger allows higher resolution. With the DigOut and DAC models, the single-bit digital inputs can be used to record 8-bit analog signals by taking advantage of the dither effect. Since these models can sample at very high rates even on slow systems, they can beat any sound card and many laboratory cards where high speed is required.
Trigger Source (in the main Trigger Menu) is set to Pulse for Sequential operation, the sweep timing is controlled entirely by Daqarta with the Trigger Cycle option. In this mode, a TTL output pulse will appear on pin 16 of the DB25 printer connector (Control port bit 2, normally Printer Init).
If Trigger Slope is Pos, this will be a high pulse that lasts the duration of the sweep unless STIM3 is also in use, in which case it will last as long as the stimulus. You can use this pulse to start an external stimulus, or you can use it as the stimulus itself by appropriate filtering, gain, or attenuation.
You can also set Slope to Neg to produce a low pulse, or Alt for alternating. In Alt mode, the Pulse output does not go off at the end of each sweep, but instead changes state at the start of the next sweep. This produces a slow square wave with a period of two sweeps.
By waveform averaging, system responses to the pulse stimulus can be greatly increased in resolution via the dither effect. The high-speed operation of the simple digital inputs on the DigOut and DAC models can thus be used to record 8-bit data or better.
Averager and/or DDisk recording by remote control. The LPTX boards are particularly friendly in this respect, since each remote control needs only a simple switch... no pull-up resistor or +5 Volt supply is required as in the usual Daqarta remote control configuration, because the printer port is already wired this way internally.
Cable center DB25 .-------------------------> Pin 1 DDisk | Remote \ Switch | `-------------------------> Gnd Cable Shield (18-25) Cable center .-------------------------> Pin 14 Averager | Remote \ Switch | `-------------------------> Gnd Cable Shield (18-25)These inputs respond equally well to normal TTL levels, if you want to have some other device or circuit operate the remote controls.
When a switch is open or the TTL level is high, the DDisk or Averager operation is halted. When the switch is closed or the TTL level is low, the respective operation may proceed normally.
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