how to generate 10KHz software clock for NI USB 6501

[AlanChen]

Hi,

I am trying to use NI6501 to send out and read in digital signal with rate about 10KHz. But since there is no internal clock for NI USB6501, I guess I have to use some kind of software clock or timing. This is something new for me and really need some help from you guys. Thank you in advance.

Alan

[AlanArmstead]

Alan,
The digital I/O of the USB-6501 is software timed. So the update rate will be dependent on a couple of things.  First, the speed of your PC, and how fast it will execute the piece of code that reads/writes to your digital ports.  Secondly, the USB bus could be the bottleneck.  Unfortunately, I don't think you are going to be able to achieve update rates of 10kHz with the USB-6501, or any other USB device for that matter.  About 1kHz update rates is the best you could expect.  This is because full speed (2.0) USB communication takes about 1 millisecond. 
-Alan A. 

[AlanChen]

Hi, Alan. A.

Many thanks for the tips. But I always heard that USB could work up to the rate something like 12Mb/s (or even 480Mb/s!). Is this rate different from the bus rate (1kHz as you mentioned)? Confused. 🙂

[AlanArmstead]

Alan,

You are correct that full speed USB has a transfer rate of 12Mbits/sec.  This is a different rate than the rate at which we can send commands to/from a USB device.  Here is a snippet of another post explaining this:   "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". 

I hope this helps to clarify.

-Alan A.

[AlanChen]

You are genius! That's pretty clear for me now. It looks USB port is not a good choice. 😞 Do you have any suggestion to realize the 10Kb/s digital IO with some ports of laptop? Thanks a lot.

[AlanArmstead]

Hi Alan,

You might want to check out the NI DAQCard-6533.  It is in the PCMCIA form factor, and it should be able to meet your needs.  Hope this helps:)

-Alan A.

[AlanChen]

A. A.

Thank you very much.

A.