Understanding Expert I/O 1000 Access Times

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I often get questions about the Expert I/O 1000’s access time characteristics. The short answer is that you can change outputs at a rate of 100Hz and you can read inputs at 50Hz. However, the complete answer is more complicated.

When dealing with MS Windows on a PC, it’s not possible to get absolute realtime results. You will always have some variability in timing. However, Dajac’s USB implementation directly associates the timing to guaranteed values in the USB specification. Therefore, we know the guaranteed worst case access times at the USB level.

Nothing prevents Windows from providing faster access, but it’s not guaranteed and will depend on such things as processor load and software implementation techniques.

Obviously, the Expert I/O 1000 is not the fastest device you’ll find, but we knew that would be the case when we designed it. A very large number of applications exist where the Expert I/O 1000 is plenty fast enough and in our experience, guaranteed latency has always been more important than raw speed. You’ll also pay a great deal more for faster solutions.

Here are access time test results. I included ADC inputs and digital I/O, but these numbers will hold for all inputs and outputs.

Sample an Analog Input
Number of Accesses: 1000
Minimum Access Time: 9475.5 us (105.54 Hz)
Maximum Access Time: 23847 us (41.935 Hz)
Average Access Time: 21519 us (46.47 Hz)

Set a Digital Output Port
Number of Accesses: 1000
Minimum Access Time: 3430.1 us (291.54 Hz)
Maximum Access Time: 15876 us (62.987 Hz)
Average Access Time: 10673 us (93.697 Hz)

Sample a Digital Input Port
Number of Accesses: 1000
Minimum Access Time: 15210 us (65.745 Hz)
Maximum Access Time: 23915 us (41.815 Hz)
Average Access Time: 21527 us (46.452 Hz)

If you have concerns about timing, keep in mind that if the Expert I/O 1000 doesn’t work for you, return it within 30 days and we’ll give you a full refund.

What other aspects of the Expert I/O 1000 would you like more detail about? Put your suggestions in the comments below and I’ll address them in future articles.