SUM of values in a comma delimited cell

I have tried to put in some of the code but I can't get it to work for me. What am I doing wrong?

Let's assume I do indeed make A1 show the following:
_A,_B,_D (I'm going to skip "C" because I have no reason, but Excel does not allow it.)
Sometimes A1 will have _A,_B or even _D,_I or even _A,_B,_E,_F,_K.

I will go down the line starting in E1, then F1, etc to define that those cells are what determine what value A through K will have. Perhaps I need to say that those cells need to define what (underscore) _A through (underscore) _K are?

I can understand the thought that I don't need the B1 expression of _A+_B+_D etc. So I'll just skip to the SUM that I want and say that B1 will simply express the SUM of the values of the letters in A1.
Do I put =EVAL in B1? Is that a formula? Is EVAL a concept that involves addition?

To clarify, _A and all the other letters could have a two digit value, one digit, 3 digit, etc. I'd like the letters to accomodate any number size. And further, any number of letters could be shown delimited in the cell, so I will need to prepare by defining out as many letters as necessary.

Maybe I'm also not using the Name feature correctly.

Sorry for the confusion.

Dan