Direct USB access from Labview?

[soeren]

A USB port cannot be comparred to a seriel port or RS232 connection, but is it possible using Labview software or similar, to have the two Data-pins of the port generate a digital on/off signal or even a PWM-signal. Is the USB communication protocol to rigid for this use?

soeren

[Jochen · Accepted solution]

Soeren,

in LabVIEW you can access the USB port directly through VISA functions, but this doesn't give you direct control over the USB lines. USB always relies on bidirectional communication, so I can't think of a way to use it as a general purpose digital output.

If you are looking for a low-cost solution for USB-based digital I/Os, you may have a look at the NI USB-6501. For fast PWM generation this device is not a good solution, as it doesn't provide hardware clocked I/O pins. Hardware clocked digital I/Os are provided by the counter/timer outputs of NI USB-621x devices and by correlated DIOs of all other M-Series devices.

I hope that helps,

Jochen Klier

National Instruments

[Intaris]

No.

The USB port is generally hard-wired with a USB controller which is a hardware device which controls detecting whether the device is Hi-speed or not (pull-down resistor).  I don't think it's really useful for what is the job of a DIO card.

AFAIK interfacint with a USB port always goes over this controller which only understands the USB protocol.

Shane.