The OP "registers" are a set of memory areas that are used as operands by the OS's floating point routines. Unless you need floating point, there shouldn't be a need to explicitly deal with them.
If you want to do math with larger integers, you basically need to write the routines yourself (precluding a library/axiom already having been written. I don't follow Axe too much.).
For example, to add the number BA (formed from variables A and B) to DC, and store the result back to BA, you could do something like A+C->A<C+B+D->B, where -> is the STO> symbol.
An easier-to-follow variation goes like this:

Code: [Select]

A+C->A
If A<C
B+D->B
Else
B+D+1->B
End

Quote from: danny90444 on July 06, 2012, 10:47:05 am

I don't understand the BA part. Is that one number split between two variables? And I don't know what floating point is exactly.

Your number A is 16 bits (2 bytes). Let's represent a bit by X. So A looks like this
XXXXXXXXXXXXXXXX.
Same for B, B looks like this
XXXXXXXXXXXXXXXX.
Now, what would be BA ? It is B followed by A so BA looks like this
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
And you just created a 32 bits number

Floating point is basically numbers with a decimal where the period is not at the same place for each number. So you could work with 53.21 and 589.4 as opposed to fixed point where the period is always at the same place for everyone