USB-8451 600us delays between reads and writes

[Bricko]

Hi Esteban,

You are correct - blue is SCL.

I'm not sure what you mean by benchmarking.  I have timed the loop in LV, and get 1 or 2ms, but of course LV can't tell me if it was less than 1ms loop time.  I realize there are a lot of levels that are handling this data, and it may be that Windows takes 600us overhead between each transmit (but I hope not).  I am trying to get data as fast as possible, so that I can use an accelerometer to show me vibration data up to 1 or 2 kHz.  I have seen very little mention of these delays, but then again I imagine most people are not trying to poll an I2C device at 5kHz. 

There is a company called Diolan (diolan.com), that claims these delays are common in USB-I2C devices, and that their own products do not have these delays.

I am interested in seeing your results with an 8451.  Thanks again for your help.

Brian

[Esteban.R]

Hi Brian

I will try to run the test on my side and I will tell you my results in the meantime here is a VI snippet  in order to measure the time that it takes execute the while loop in other words the time that it takes to read the values lest see if the execution of the code

Regards

Esteban R.

[Bricko]

Hi Esteban,

I get times between 1-2 ms, usually averaging around 1.7-1.9ms.

Interested in seeing your results.

Thanks,

Brian

[GPIB_Guru]

SCL is being held low, which indicates that this is caused by the device (it is clock stretching).

What is your connected device?