How can I delay for 1 microsec on my F2808? I need a 1 microsec pulse on a GPIO out.

Question

Submitted by Joe on Tue, 03/22/2011 - 20:35

I need a 1 microsec output pulse on a GPIO out pin. I will need to set the pin low, delay 1 microsec, then set it high. I know there is a NOP instruction which takes 1 tick. How to I use that?

Altair Forum User · Answer

Submitted by Anders89 on Tue, 03/22/2011 - 20:43.

You can use the externFunction block to create a small delay loop by putting the following C loop into it:

{ int a; for (a=0;a<10;a++) asm('NOP');}

Note that though the chip clock is 100 MHz, the loop count is only to 10. That is because one loop iteration takes 10 ticks due to an 8 tick pipeline stall + 1 tick NOP + 1 tick inc/compare loop counter.
  Then write a 0 to the GPIO above the NOP delay, and write a 1 to the GPIO below it. VisSim generates code for parallel flows in top down order, so you will get a 1 microsec low pulse.

See attached diagram below (you must be logged in to see it).

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