NI 8451 DIO/GPIO speed too slow!

Hi all,

I'm using NI 8451's DIO (digital !/O interface) to create a signal pattern. I use a for loop to output 30 loops of '1's and '0's. Inside the for loop, I simply use a '8451 write to port' function. My problem now is the each for loop execute too slow (4ms) for my application. 8451 should be able to go faster than 4ms per data (e.g the 8451 SPI port is way faster), so is there anyone know how to speed up the for loop or make my digital output faster?

Thanks!