I'm still trying to understand your Task and your Hardware.
Let's consider outputting one row, say 0000 0001 0010 0011. There are 4 4-bit "registers" here, and you speak of 4 DO "lines". Now, in DAQmx, a Digital Output "line" means a single bit for what is usually a Digital Output Port that can variously be configured to consist of 4, 8, 16, or 32 bits, or "lines". When you do a DAQmx Write to a Digital Output, you write the entire "unit" all at once. If you have configured the the DO as a Port, then you write a U8, U16, or U32 to it and all of the bits are set at the same time. If configured as multiple Lines, you can write a single Channel and manipulate one Line, or multiple Channels and do them all together.
I have no idea which scenario you are using. Given that you are writing 4 4-bit quantities at a time, I also am unclear (this is basically the same question as above) if you want to write them a bit at a time (say 1 bit per second), in groups of 4 bits (or a 4-bit "simultaneous write" at 1 group a second) or all 4 groups of 4 bits at the same time (again, at 1 group-of-16 a second). [i"m keeping the "update" rate fixed at 1Hz for convenience).
Once we clarify this, the next bit, doing this over and over with a cyclic pattern of 4 "rows" of (4 columns of 4 bits each) is very simple. There are multiple ways to cyclically "pull out" a row from a 2D array -- the simplest is to take the Loop index ("i"), pass it through the Remainder/Quotient function with divisor of 4, and use the Remainer to Index Array and return the selected row. It will return 0, 1, 2, 3, 0, 1, 2, etc. Now send this to your DAQ (where you'll do the timing, easy once you clarify what you are going to do with the Row and the so-far-mysterious DAQ Hardware).
Bob Schor
