down counter question

[Evan A Young]

I am working on a project that requires me to output a number that is decrementing at a user defined speed (velocity). I need to decrement a number and write it out to a digital port. For all purposes, the number will start at a user defined value, and decrement according to the user defined velocity.

The problem is, I need to get up to 16000 decrements per second. That would mean that I would need a loop that can excecute at 0.0625 ms per loop. That seems unrealistic. Is there another option to do this? Is there some sort of IO that will let me choose a value to start at and count down at a given frequency?

I have looked at the coutners in labview, but I need to output the current number(height) onto a port (8 bit binary numbe
r).

I have an example attached of the process as I have it now. Seeing as the "wait for next multiple of" function is only accurate to about 1ms, I can only get up to a velocity of around 1000 m/s. As I stated above, I need to get to around 16000 m/s.

Am I confusing anyone yet?

Thanks for your help,
-Evan

[Filipe A.]

Hello;

The best option you have to accomplish that task is by using one of the boards of the 653x family. Those are digital boards in what you can execute pattern output operations. That means you will program a buffer in a way its first element is the first number to be output, the second element is that number decremented by one, and so on. Then, you can program the clock rate of that board so those numbers can be clocked out to the digital lines. With those boards, you have the option of outputing 8-bit, 16-bit or 32-bit words, in parallel, by each clock cycle.
Regarding the speed, since you will be clocking those numbers in hardware, and those boards can support a clock pulse train up to 20MHz of frequency, you should be ok on outputing words at the mentione
d rate.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments