Can USB be used as a poor man's digital output?

[AustinMcElroy]

If I need to generate a 130MHz TTL or LVTTL clock signal, is it possible to use USB for this?  How would I go about programming the USB port in Labview?

Thanks,
Austin

[smercurio_fc]

USB was not designed to do this. You're better off getting a cheap USB DIO module. NI sells a few, and you can get some from other vendors as well.

[AustinMcElroy]

Which model runs at high frequencies (100MHz and higher)?  

Thanks,
Austin

[smercurio_fc]

See for yourself: http://sine.ni.com/nifn/cds/view/main/p/sn/n14:7562,n24:USB,n3:7691/sb/%2Bnigenso12/lang/en/nid/1036/ap/daq
 

[lmtis]

For a tighter budget try:
 http://www.measurementcomputing.com/cbicatalog/directory.asp?dept%5Fid=224&top%5Fid=22&dept%5Fname=PCI&mscssid=Q6WEXC1HSL5E8MTT7PWDTR3C3V9K6K24


Message Edited by lmtis on 05-20-2008 10:13 AM

[AustinMcElroy]

Thanks for the fast feedback, but I am not finding any boards from the sources that y'all provided that can hit 100Mhz. 


Thanks,
Austin

[GerdW]

Hi Austin,

USB1 was designed for (something at) 12Mbit/s, USB2.0 added 480Mbit/s. So USB1 gives you a raw data rate of 1.5MB/s, USB2 60MB/s. This includes all handshaking/addressing overhead.

A TTL output usually is a 8bit wide parallel port. You want to output data at >100MHz hence you need a data rate of (atleast!) 100MB/s. This will not be possible with (standard) USB!
Better use some PCI/PXI/cRIO equipment...

I remember a NI seminar about choosing the right port/bus system for your measurements... You should find a presentation on this topic in the "Academics" section of NI's website!


Message Edited by GerdW on 05-20-2008 05:37 PM

[smercurio_fc]

Sorry, misread your frequency requirement. NI doesn't have a USB product to fit that. You would need to go with a plug-in board, like the NI-5404.

EDIT: Was looking up product info while GerdW responded in which he said a similar thing, so you'll need to look at an alternate solution.

Message Edited by smercurio_fc on 05-20-2008 10:49 AM

[Matthew_Kelton]

If you're just generating a clock and not data, then just buy an oscillator.

[G_Lo]

Austin,

A High Speed Digital Waveform Generator is possibly an option as well.  More specifically, PCI-6552, PXI-6552, PCI-6542, and PXI-6542 have the ability to perform both TTL and LVTTL with a maximum clock rate of 100MHz.  Please keep in mind that the clock rate will change with the logic level.  For example, TTL will result in a clock rate of 50MHz while LVTTL will cause a 50MHz to 100MHz clock rate.