DIO/Counter for high speed switching???

[capsys]

Iam acquiring data from the O/P of a MUX(32 i/p)s via an analog I/P ch.In a parallel loop i have to change the address of the MUX using 5 DIO lines at a rate of 10 KHz(at least 1 KHz).since this rate of switching is difficult to achieve with DIO write in S/W loop,i'm planning to use a counter.In that case i need an intermediate circuit which takes counter pulses(at 10KHZ) as clock and generates address from 00000 to 11111.can anyone help me please????A high speed DIO will be too costly for this simple application

[rgharrison]

Hi,

From what I understand, you want to be able to control the address lines of the MUX at 10kHz using a standard DAQ board. You are correct in that the high-speed digital boards (NI-653x) boards can handle this type of application but there is no way for the standard DAQ board to handle this.

If you are allowed to address the address lines of the MUX in sequence (1,2,3,4 etc..) you can use the pulse train of a counter to source an external counter where the count lines are exposed. The problem is that the count lines on the NI DAQ boards are not exposed for use and thus you can't access them.

There is however another...
You can use 2 counters and the onboard frequency generator of the DAQ board (assuming you have an E Series) to control the faste
st switching 3 bits. What you will need to do is program the frequency generator (Freq_out counter) with a frequency of 10kHz and then program counter 0 with a 5kHz frequency and counter 1 with a 2.5kHz frequency. Then you can use a fast software loop to change the highest order 2 bits at rates equivalent to 1.25kHz and 625Hz using 2 digital lines. That will give you the rates you need and still have 5 bits. This solution is a little convoluted but it should work if your software timers for the digital lines are working accurately enough and at rates of at least 1.25kHz. you can obviously step down your rate and have your counters start from 1kHz and work down to 62.5Hz. Anyway, hope that helps. Have a good day.

Ron
Applications Engineer
National Instruments