What sample rate can I achieve with the USB-8451?

[gahouck]

To whom,

              I have a USB-8451 communicating with an ADC through SPI. Using the labview script configure and run functions, I have verified that the CLK and the CS perform as required. The data returned on the SDI pin appears correct. I can read the data and convert it. Now the qustion is, how fast can I run it? My testing, so far, indicates that I can only sample at a rate of 1 sample every 1mS. Does that sound about right?

             My ADC is a slave that is triggered on the chip select. The negative going edge starts a conversion. As you clock it, the data is returned. The chip select is then sent high and then the process repeats. The whole SPI package process takes about 70uS to complete, except then there is a 900uS of dead time until the next CS. Is that what is to be expected? 

Thanks

Greg 

[John E]

Hi Greg,
It sounds like you are looking for a way to speed up your sample rate.  Some things to look at are:
What is the clock rate of your 8451?
What is the clock rate of your ADC?
Are there any other things that could be slowing it down?

Regards,

[raldo]

I'm evaluating an NI-8451 OEM unit for use on WinXP with the C Api.

I'm seeing the same behavior as the user that created this thread. To answer the questions that John E answers gahouck's post with:

o What is the clock rate of your 8451: 12Mhz

o What is the clock rate of your ADC?: 12 Mhz

o Are there any other things that could be slowing it down? I don't think so.

I've been transmitting data in small chunks (4 bytes), both using the advanced API and the basic API. With Both these methods I obtain a sampling period of 1-2 milliseconds.