Thanks Steve:

The bottom line is. Say if I want to set Bit 2 at the first byte located at 0xC200 I would simply call my write_output function with write_output(3,1), For the same bit located on the next byte it would be (11,1). I have three bytes of i/o at two different addresses which I'm indexing contiguously.

Even though all of my pointer arithmetic and bit shifting is workng correctly my final call below is not accessing the hardware.

valve = (valve or mask);

I suspect that valve is not being addressed properly in set_ouput declaration.

set_output: procedure(ptr, mask, state);
declare ptr word, mask byte, state byte;
declare valve based ptr byte;