I want to create a TTL pulse. The stepper motor I'm trying to control responds to a high to low edge, when the low pulse width is greater than 0.5 microseconds. What is the best way to go about creating a pulse like this?

[Scott Allen]

I'm using the NI PCI-6025E card connected to an SCB-100 wiring peripheral. I'm programming the DAQ card using LabVIEW 6.0.2 on a win95 box.

My first attempt has yielded some surprising results.

I created a vi with a single while loop set to true. Within that while loop is a two frame sequence. Both frames use the "Write to Digital Line.vi".

The first frame sets the line in wire to false.

The second frame sets the line in wire to true.

The device channel on both frames has been set to my user defined channel nam
e -> clock.

clock --> sets the DIO0 channel to be digital write out.

Using an oscilloscope and some wires I hook ground to the SCB-100's digital ground and I hook the probe to the DIO0 channel. What I see are two different pulses alternating between one another. One has a pulse width of 5ms and the other has a pulse width of about 50ms. You seem to get a grouping of one type of pulse followed by a grouping of the other type of pulse.

Obviously this is very strange and not what I want. It is also far too slow. So I'd like to know if anyone knows how to do this properly. Remember I only need a low pulse width of 0.5 microseconds.

Thanks,

Any help or guidance would be much appreciated.

Scott

[Erin_B.]

Scott,

You don't need to use a digital line to create a TTL pulse. The PCI-6025E has two onboard general purpose counters. You can use one of these counters to create a single pulse of the desired pulse width. For an example of how to program the counters on your board, refer to LabVIEW's Search Examples>>I/O Interfaces>>Counters>>Pulse Generation>>DAQ-STC based.

The advantage of using a counter over the digital line is that it allows you to control the timing of the pulse through hardware and not software. Thus, it is inherently faster, and the timing resolution is more accurate. The counter will count down an internal 20 MHz timebase to create the pulse delay and the pulse width.

For more information on the hardware capabilities of your board, you can refe
r to the User Manual online at www.ni.com/manuals.

Hope this helps.

Regards,
Erin