How to increase the Speed of USB Devices (6501 and 6009)?

[RodrigoCésar]

Hy guys!

My question is:

In datasheets of the USB devices, the only reference about the speed of these boards is the Bus Interface speed (12Mbit/s). But in my application (i'm trying to use delphi to control the device), each instruction, doesn't matter if is a write or a read function, is taking 1ms to execute. Could i increase this speed?? What could be wrong?

OBS: I updated the Ni-DaqmxBase 1.4 to the new NI-DaqMx 7.5, and notting has changed.

Functions used:

istatus := DAQmxWriteDigitalU32(TaskEscrever, 1, 0, -1, DAQmx_Val_GroupByChannel, @writedata,nil, nil);

istatus := DAQmxReadDigitalU32(taskLer, -1, 10, DAQmx_Val_GroupByChannel, @readdata[j], 1,nil, nil);

[Irene He]

Hello,

The two usb DAQ from NI are full speed interface (as you said 12M/s bus speed). The full speed interface has a frame size of 1ms, the root hub transmits a packet every 1.0 ms and this is the minimum time that you can read/write from/to usb device, normally because of the windows scheduling, 1ms is very tight, windows may miss it in some occasions, some usb device designers would prefer to use something between 2ms - 10ms polling period, which means some devices may even react to commands within 2ms - 10ms. But it looks like the two NI usb DAQ use the 1ms polling period and that is the shortest time you can get in software paced mode. If you need very fast digital update rate, you may need to look at PWM output, it generates digital pulses at very fast rate as the link given below, the iUSBDAQ - U120816 can generate PWM pulse from 3kHZ - 333kHZ.

NI USB DAQ maybe good, but it wouldn't hurt to look at some other company's product too. the below link of usb daq gives the best price/performance ratio, LabVIEW vis are very easy to use and you avoid the pre-configuration in a separate application for DAQs which sometimes may be big deal if your customers are not engineer or scientist, but regular computer users. You are welcome to compare.

http://www.hytekautomation.com/Products/IUSBDAQ.html

Thank you.

Irene

[Irene He]

Hmm... I see my post gets one star. Well, if you have opinion or have anything to say to correct my post, please welcome to post it here. Not just put one star and run.

Thanks.

Irene He