daqmx write (raw 1D U8) schneller als 4ms? (DAQpad 6016)

[LeXx]

Hallo

Ich habe eine Frage bezüglich dem VI DAQmx Write. Ich versuche mit diesem VI auf die digitalen Ausgänge

des DAQPads 6016 zu schreiben. Ich verwende dafür die Eigenschaft: Raw 1D U8 um ein Array auf Port0 zu schreiben.

Dies ist auch kein Problem, jedoch ist das Ganze zu langsam. Pro Bit das ich ausgebe, messe ich mit dem KO ca. 4ms.

Nun zu meiner Frage, gibt es eine Möglichkeit mit höheren Frequenzen auf die digitalen Ausgänge zu schreiben?

(Mein Ziel: Über SPI mit dem DAQPad 6016 ein EEPROM zu betreiben. =>pro Byte ~40ms, das EEPROM zu beschreiben dauert ewig)

Vielen Dank

LeXx

[JoGrMu]

Hello LeXx,

could you please post the code you use to write to that port here? It would be helpful.

Have you looked into the shiped examples yet (e.g. Write Dig Chan-Int Clk-Dig Start)?

Regard

Johannes Gräper

Applications Engineering

NI Germany 

[LeXx]

Hello

Sorry, that I couldn't write earlier.

I tryed most of the standard examples from LV 8.6. Now I'm not sure wheater I did something wrong or

it's not possible to do it faster. The VI DAQmx Write (RAW 1D U8) was after my measuers the fastest (4ms/Bit).

As I used the other examples (for example yours: write dig chan....) I always got some errors with the property nodes:

"Possible reason(s):

Measurements: Requested value is not a supported value for this property.

Property: SampTimingType
You Have Requested: Sample Clock
You Can Select: On Demand, Handshake"

or I couldn't see any effects when i changed the nodes.

Thanks

[Brad_K]

Hello LeXx,

The DAQPad-6016 DIO only supports on-demand and handshaked timing. Handshaking is probably not going to help you implement a SPI master, and the DAQPad specifications say that handshaked DIO has a max transfer rate of 250 S/s, which is still 4 ms per sample anyway.

Does your USB controller show up in Device Manager as a Universal Host Controller Interface (UHCI)? It takes DAQmx 4 ms to send each message to the DAQPad using a UHCI controller. I seem to remember from DAQPad development that OHCI (Open Host Controller Interface) controllers are slightly faster for this use case, more like 1-2 ms. Installing an OHCI add-in card may help slightly, but finding one would probably be difficult, since most USB add-in card manufacturers don't print "UHCI" or "OHCI" on the box. Installing an OHCI add-in card is also unlikely to be a viable option if you're using a laptop.

What is your performance goal? In order to achieve it, you may need to use a different data acquisition board, such as a USB M Series (which supports sample clock for DIO) or a PCI/PXI M Series (which has lower latency than USB).

Brad

Message Edited by Brad K on 02-26-2009 10:49 AM